Chemical Physics

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Chemical Physics - Abstracts

Experimental demonstration of a microwave non-thermal effect in DMSO-NaCl aqueous solution

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Wenyan Tian, Zemin Li, Li Wu

Abstract

In this paper, a special experimental system was elaborately designed to probe the existence of microwave non-thermal effect. Based on the experimental system, the resistance of solution was precisely measured during microwave irradiation. In order to make a comparison with the results of microwave irradiation, resistance and electrical conductivity were respectively measured with the same experimental system and electrical conductivity meter under conventional water bath heating. Results showed that the resistances were all decreasing with temperature rising during conventional heating process, which was contrary to the results of microwave irradiation method. It proves the existence of a microwave non-thermal effect.

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Judd-Ofelt parametrization from emission spectra: The case study of the Eu<sup>3+ 5</sup>D<sub>1</sub> emitting level

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Aleksandar Ćirić, Stevan Stojadinović, Mikhail G. Brik, Miroslav D. Dramićanin

Abstract

Traditional applications of the Judd-Ofelt (JO) theory to the analysis of the Eu3+ optical spectra make use of the emission transitions originating from the 5D0 manifold. In the present paper, we report an alternative method of evaluating the JO intensity parameters from the Eu3+ emission spectra based on the 5D1 → 7F0,1 transitions. The reduced matrix elements of the unit tensor operators are re-calculated for the 5D0,1,2 → 7F0,1,…,6 Eu3+ transitions in the intermediate coupling approximation using the average electrostatic and spin-orbit coupling parameters. The suggested method was tested by analyzing the emission spectra of the Eu3+ doped GdAlO3, LaF3, NaYF4, Y2O3, ZrO2, YNbO4, ZBLA and PIGLZ hosts. It is shown that the developed method is more accurate for the hosts with relatively high 5D1 level population, which emphasizes its high potential and applicability. In addition to the JO analysis, the CIE chromaticity coordinates are calculated for the investigated spectra.

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Study of the electronic structure and absorption spectrum of Co and H doped ZnO by first-principles

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Qingyu Hou, Wenling Li, Zhenchao Xu, Yajing Liu, Shulin Sha

Abstract

The redshift and blueshift of the absorption spectrum of Co-doped ZnO have been reported experimentally. The effects on the bandgap and absorption spectrum of Co doping and interstitial H coexisting in ZnO have not been fully elucidated. The electronic structures and absorption spectra of Co-doped ZnO, interstitial Co-doped ZnO, and supercell model with four different spacings of substitutional Co and interstitial H co-doped ZnO systems were calculated using first-principle analysis. Results indicated that the multibody effect of the doped systems is greater than Burstein–Moss effect. The bandgap of the doped systems is narrowed, and the absorption spectra are significant and presented in order as follows: ZnO < Zn0.9722Co0.0278O < Zn0.9583Co0.0417O < Zn0.9583Co0.0417Hi0.0417O < Zn0.9583Coi0.0417O.

Graphical abstract

Band structure and total state density: (e) Zn0.9583Co0.0417Hi0.0417O.

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Interplay of exciton annihilation and transport in fifth order electronic spectroscopy

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): C. Heshmatpour, J. Hauer, F. Šanda

Abstract

Multidimensional fifth order spectroscopy is a sophisticated and specialized tool for probing bi-exciton dynamics. The complexity of the signals emitted into $±2K→1∓2K→2+K→3$ directions calls for a detailed theoretical treatment of 2D line shapes, including both exciton-exciton annihilation and intraband relaxation dynamics. Based on a master equation formalism, we discuss the signal’s temporal evolution and clearly distinguish between intraband transport within first and second exciton manifolds. We prove analytically that signatures of single exciton transport vanish from spectrally integrated signals of parallel homo-aggregates of arbitrary length, while transport within the second manifold accounts for the diffusion limitations of annihilation. In an effort to model fifth order electronic spectra of tractably small systems, we develop a dynamical model for molecular dimers and trimers. We show that fifth order two-dimensional spectroscopy allows to track and pinpoint population transfer- and annihilation dynamics of bi-excitons, without the need to perform and analyse intensity dependent experiments.

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The analysis of charge transport mechanism in molecular junctions based on current-voltage characteristics

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Xianneng Song, Bin Han, Xi Yu, Wenping Hu

Abstract

We report here a theoretical model study of the current-voltage (I-V) characteristics of tunneling and hopping transport in molecular junctions. We found that the I-Vs of the two types of transport have very different shape characteristics. The I-V in tunneling transport is in near-linear relation at low bias, while is exponential for the hopping transport. The current in hopping transport thus can span a much wider range at semi-logarithm scale than tunneling transport, which can be used as an intuitive guide in analyzing the transport mechanism. The idea is supported by series of experimental studies reported before by Frisbie et al. where a clear I-V characteristic change can be seen when transport mechanism changed from tunneling to hopping. The two theoretical models were further used to fit the reported experimental I-V data, and we found that the transport mechanism obtained by the model is in consistence with the experimental conclusion. Moreover, our method also revealed the coexistence of two transports during the tunneling-to-hopping transition, and the contribution of the two channels to the current is bias dependent. Our research thus provides a new powerful theoretical method for the study of charge transport mechanism in molecular junctions.

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Thermoelectric transport properties of magnetic carbon-based organic chains

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): F.X. Tan, L.Y. Yang, X.F. Yang, Y.S. Liu

Abstract

We propose a perfect spin-caloritronics device based on a carbon-based organic chain. A spin-semiconducting property is achieved, which originates from the edge localized states. The appearance of spin-dependent transport gaps results in a large spin Seebeck coefficient. Moveover, the dimensionless spin thermoelectric figure of merit (FOM) at room temperature can be enhanced to as high as 35. Furthermore, the pure spin current or single-spin current can be produced at some chemical potentials under a temperature difference, and their transport directions can also be tuned by the chemical potential. Therefore, the carbon-based organic chain is well suited for designing the multifunctional spin-caloritronics devices.

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The charge and spin thermoelectric FOMs as functions of the chemical potential.

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Tuning of structural and magnetic properties by intriguing radical-radical interaction by double electron oxidation in U-A-U′ triplex formation

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Snehasis Bhunia, Aditya Kumar, Animesh K. Ojha

Abstract

The spin coupling properties of a series of two di-radical centers AU and AU′ in U-A-U′ triplex were investigated. These two series are considered by intriguing the radical-radical cation (A+U+ and A+U′+), radical-dehydrogenated (A+U(-H1), A(-H1)U+, A(-H1)U′+ and A+U′(-H1)), and dehydrogenated-dehydrogenated (A(-H1)U(-H1) and A(-H1)U′(-H1)) as RNA base couplers. The structural and electronic properties were calculated employing density functional theory (DFT). The di-radical character was identified by performing DFT and complete active space self-consistent (CASSCF) calculations. The calculated value of coupling constant revealed the presence of both types of magnetic interaction i.e. ferromagnetic (FM) and anti-ferromagnetic (AFM). A strong magnetic interaction is found for the radical-dehydrogenated A(-H1)U+ series whereas a weak magnetic interaction is observed for radical-radical cation, A+U+, A+U′+ and other di-radical series e.g. A+U(-H1), A+U′(-H1), and A(-H1)U′(-H1). The transformation of FM and AFM coupling with the change in dehydrogenation sites is explained with the help of distribution of spin density.

Graphical abstract

The formation of di-radical via oxidation or ionizing radiation causes to induce magnetic interaction without disrupting the structural stability. For this kind of ionized structure, the energy of HOMO-LUMO gap is so small that most of the outer orbital electron can move easily to LUMO and thereby form SOMO which has lower energy compared to HOMO.

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Dissociation and localization dynamics of charge transfer excitons at a donor-acceptor interface

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Hong-Guang Duan, Ajay Jha, Vandana Tiwari, R.J. Dwayne Miller, Michael Thorwart

Abstract

We study the quantum dissipative dynamics of charge transfer excitons localizing and dissociating at the interface of a molecular heterojunction typical for organic photovoltaics. The excitons dynamics can be separated into a short-time regime with short-lived electronic coherence and a long-time regime with a slowly decaying incoherent dynamics. On the short time scale (<300 femtoseconds), the excitons are coherently delocalized along the molecular chain. On a long time scale (few picoseconds), charges get localized and relax to the lowest-energy charge transfer state. However, the long-time dynamics still involves excitons which are delocalized along the chain. This is favored by the strong coherent mixing of states on the charge transfer manifold. Furthermore, molecular vibrations dramatically hamper electron-hole separation. Our work thus may motivate the design of new materials with a more rigid molecular backbone.

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Structures and stabilities of glycine and water complexes

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Junyan Sun, Zhuo Xu, XiaoJie Liu

Abstract

Structural elucidation, stability, properties and proton transfer processes of neutral and zwitterionic Gly(H2O)1-6 complexes are studied by ab initio calculations. Polarizable continuum model (PCM) is important for energy examination since solvent effects is sensitive to the energy. Glycine is fully solvated by five discrete water molecules under polarizable continuum model (PCM). The structure of neutral and zwitterionic Gly(H2O)1-6 complexes changes from a ring motif to a chain motif, and then to a cubic motif. The binding energy for neutral and zwitterionic Gly(H2O)1-6 complexes increases linearly as function of the number of water molecules increase, indicating Gly(H2O)1-6 complexes exhibit relatively higher stability. However, distortion of water molecules will cost more energy, leading to reduced binding energy per water molecule. The reduction is mainly attributed to the directivity and saturability of H-bonds. Importantly, we find the deprotonation of –NH2 for zwitterionic Gly(H2O)2-4 needs ~10 kcal/mol, which is consistent with the experiments.

Graphical abstract

Gly(H2O)n complexes structure changes from a ring, a chain and then to a cubic motif.

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Morphologically controlled synthesis, characterization and application of zinc-aluminum layered double hydroxide nano needles

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Saba Jamil, Shanza Rauf Khan, Afaaf Rahat Alvi, Farhana Kausar, Shahid Ali, Safyan A. Khan, Mohd Naim, Aneela Malik, Muhammad Ramzan Saeed Ashraf Janjua

Abstract

Zinc-aluminum layered double hydroxide (Zn-Al LDHs) nanoparticles are prepared by a solvothermal method. To study and investigate the morphology and properties of prepared Zn-Al LDH nanoparticles, nanoparticles are subjected to different instrumental techniques. It is clear from X-ray diffraction pattern, the product is composed of cubic unit cell, highly pure and crystalline. Data obtained from XRD analysis is further subjected to different softwares to understand the crystal structure and atomic coordinates. The lattice is studied in different orientations to understand the possible arrangements of atoms within unit cell. By scanning electron microscope (SEM) and transmission electron microscope (TEM), it is observed that the synthesized Zn-Al LDH product is dispersed needle like, regular in shape with compact structure, sharp needle like boundary with a size of approximately 50–150 nm. The synthesized nanoparticles are used as additive for combustion characteristics (flash and fire points) and physical characteristics (cloud and pour points, kinematics viscosity and specific gravity) of crude kerosene oil.

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Volt-ampere characteristics of porcine retinal Müller cell intermediate filaments

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Abstract

In the current study we reported current-voltage (I/V) characteristics of Müller cell (MC) intermediate filaments (IFs) isolated from porcine retina. It was found that the measured I/V dependences demonstrate behavior of a semiconductor in contact with metal (Au) electrodes. The analysis of the temperature dependence of the experimental I/V curves produced estimates of the parameter values characterizing the electrical conductivity properties of the studied MC IFs. The I/V characteristics and the parameter values allowed to describe the MC IFs as a semiconducting material. The observed properties clarify the mechanism of high-contrast daylight vision of vertebrate eyes. This mechanism was extensively discussed earlier, and is directly dependent on the electric conductivity properties of MC IFs.

Significance Statement

Retinal cones and rods are physically connected to glial Müller cells by intermediate filaments (IFs). Electric conductivity of IFs allows for a simple quantum mechanical description of light energy transmission through the retina, providing a convincing mechanism that achieves high-contrast vision in vertebrate eyes. Note that classic light transmission is hindered by light scattering on the retinal structures. Electric conductivity of IFs also opens the possibility for energy exchange within and between other cell types by way of IFs and microtubules, and the possibility that such structures may be used for signaling e.g. in the nervous system.

Graphic abstract

Ampere-voltage dependence measured for Müller cell (MC) intermediate filaments (IFs) adsorbed by the gold electrode matrix placed into the MC IF suspension with the nIF = 3.2 × 108 cm−3 initial number density of the IFs. We carried out the I/V measurements after 800 s delay, necessary to reach an equilibrium between the IFs adsorbed by the electrode matrix and those suspended in the water.

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Comparison of moving and fixed basis sets for nonadiabatic quantum dynamics at conical intersections

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Evgenii Titov, Alexander Humeniuk, Roland Mitrić

Abstract

We assess the performance of two different types of basis sets for nonadiabatic quantum dynamics at conical intersections. The basis sets of both types are generated using Ehrenfest trajectories of nuclear coherent states. These trajectories can either serve as a moving (time-dependent) basis or be employed to sample a fixed (time-independent) basis. We demonstrate on the example of two-state two-dimensional and three-state five-dimensional models that both basis set types can yield highly accurate results for population transfer at intersections, as compared with reference quantum dynamics. The details of wave packet evolutions are discussed for the case of the two-dimensional model. The fixed basis is found to be superior to the moving one in reproducing true nonlocal spreading and maintaining correct shape of the wave packet upon time evolution. Moreover, for the models considered, the fixed basis set outperforms the moving one in terms of computational efficiency.

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Structural, optical and electronic properties of CuO and Zn doped CuO: DFT based First-principles calculations

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Meherun Nesa, Md. Abdul Momin, Mehnaz Sharmin, A.H. Bhuiyan

Abstract

Density functional theory based First-principles calculations have been performed to investigate the structural, optical and electronic properties of CuO and Zn doped CuO and compared with experimental results. Calculations are demonstrated by Cambridge Serial Total Energy Package. Calculated values of lattice parameters matched 80% with experimental data of CuO and for Zn doped CuO, there was a 55% match. Figures of electronic band structure, TDOS and PDOS have been computed from the electronic structure of CuO and Zn doped CuO. Significant transition occurs in band gap after Zn doping. Optical properties showed that CuO and Zn doped CuO were transparent, having a small energy gap and maximum reflectivity at infrared region. The real part of refractive index was higher at lower energy region and imaginary part of refractive index was zero at 28 eV photon energy. The calculated value of band gap was in good agreement with the experimental value.

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Kinetics and oxidation mechanism of pyrene initiated by hydroxyl radical. A theoretical investigation

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Maryam Nayebzadeh, Morteza Vahedpour, Abolfazl Shiroudi, Joaquim M. Rius-Bartra

Abstract

Oxidation mechanism of Pyrene (Py) by OH radicals is studied in two possible reactions by density functional theory (DFT) at the M06-2X/6-311++G(2df,2p) theoretical level. OH-addition reaction in compare with the H-abstraction reaction is a more favored pathway in the gas-phase. Hence, the studies continued for investigating the kinetic aspects of the OH-addition reaction. Furthermore, Rice-Ramsperger-Kassel-Marcus (RRKM) theory as well to calculate the kinetic rate constant for the initial steps and investigate the effects of diversity in pressure and temperature. Pathway 2 (attack onto C2 carbon atom) and following that forming of the related complex which has a lower energy barrier is the most efficient process. The good agreement with the available experimental data reveals that a two-step reaction scheme prevails. These ratios also show a decrease in the regioselectivity by increasing the temperatures and decreasing the pressures. The Pyrene lifetime in the atmospheric condition with OH is estimated ∼5.5 days. An atom in Molecules theory (AIM) in critical point and natural bond orbital (NBO) analysis use to describe the nature of covalent interaction, and is as a confirmation of DFT. The NBO analysis shows a decrease in the HOMO-LUMO gaps to form the stable complex, which is parallel with the decreasing of activation energy.

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Facile synthesis of WO<sub>3</sub> micro/nanostructures by paper-assisted calcination for visible-light-driven photocatalysis

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Linyan Zhao, Xiaoli Xi, Yangsi Liu, Liwen Ma, Zuoren Nie

Abstract

WO3 micro/nanostructures were synthesized by a facile paper-assisted calcination method, which combined the merits of wet chemical and thermal decomposition. The morphology of WO3 micro/nanostructures can be varied by adding inorganic ions. Various microscopic and spectroscopic techniques were employed to characterize the WO3 micro/nanostructures. Methylene blue (MB) photodegradation experiments showed that the WO3 micro/nanostructures possess excellent visible-light-driven photocatalytic ability, and the excellent photocatalytic abilities (up to 95%) of WO3 micro/nanostructures under visible light irradiation seem corresponding to oxygen vacancies, band gap value and surface area etc. The method in this work shed light on convenient fabrication of micro/nanostructured materials for environmental remediation.

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Molecular level insight into the counteraction of trehalose on the activity as well as denaturation of lysozyme induced by guanidinium chloride

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Biswajit Biswas, Prashant Chandra Singh

Abstract

The effect of trehalose on the activity and structural change of lysozyme induced by the chemical denaturant guanidinium chloride (GdmCl) has been investigated using the activity assay, spectroscopy as well as molecular dynamics simulation methods. The activity along with secondary and tertiary content of lysozyme decreases drastically in the presence of GdmCl whereas the addition of trehalose in GdmCl reverses the effect. It has been observed that the addition of trehalose in GdmCl affects mainly to the active site of lysozyme unlike the case of urea in which water gets accommodate at the surface of the protein. This study suggests that addition of trehalose in GdmCl changes the solvent environment more like to the native condition in the active site of lysozyme and modifies the electrostatic and Lennard-Jones interactions which play an important role in the reversal of its activity as well as structural change.

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Enhanced photocatalytic performance of Nd<sup>3+</sup>-doped TiO<sub>2</sub> nanosphere under visible light

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Jicai Liang, Jingya Wang, Kaifeng Yu, Kexian Song, Xiaofeng Wang, Weiping Liu, Jiazi Hou, Ce Liang

Abstract

Nd3+-doped TiO2 nanosphere is synthesized by template-free method (recombined coprecipitation with hydrothermal method), which possesses anatase TiO2 and TiO2(B) nanosphere structure produced during hydrothermal process. After doping different content neodymium ions, the excellent photocatalytic performance of doped samples have been confirmed by subsequent photodegradation experiments, in which the 1.0 mol% Nd3+-TiO2 sample has been considered the optimum choice owing to its high degradation of 99.14% under visible light irradiation in 120 min, it almost completely degraded methylene blue in 80 min under simulated sunlight. This conclusion is contributed to further industrial application of TiO2 in the degradation of sewage.

Graphical abstract

Nd3+-doped hollow TiO2 samples are synthesized by a template-free method, and display excellent photocatalytic performance. The 1% Nd3+-doped TiO2 sample exhibits the highest degradation rate of 99.14%, which has almost completely degraded methylene blue in 80 min under simulated sunlight.

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Swelling pressure of Na- and Ca-montmorillonites in saline environments: A molecular dynamics study

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Bukunmi Akinwunmi, Janne T. Hirvi, Seppo Kasa, Tapani A. Pakkanen

Abstract

The swelling pressure of bentonite clay is an important characteristic that influences its use in nuclear waste disposal repositories. A molecular dynamics study was performed to investigate the influence of salt solutions of different concentrations on the swelling pressure of Na-montmorillonite and Ca-montmorillonite in NaCl and CaCl2 solutions, respectively. Na-montmorillonite shows a gradual increase in swelling pressure as the dry density increases, while Ca-montmorillonite shows a slow increase as the dry density increases, after which a steeper increase in swelling pressure was observed. There is an overall decrease in swelling pressure of Na- and Ca-montmorillonites as the salinity of the surrounding solution increases. The influence of ionic strength was most prominent for Na-montmorillonite at moderate to high dry densities. At low to moderate dry densities, the swelling pressure of Na-montmorillonite was greater than that of Ca-montmorillonite; however, at high dry densities and ionic strengths, Ca-montmorillonite exhibits the higher swelling pressures.

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Applications of neural networks to dynamics simulation of Landau-Zener transitions

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Bianjiang Yang, Baizhe He, Jiajun Wan, Sharvaj Kubal, Yang Zhao

Abstract

We simulate the dynamics of a qubit-oscillator system obeying the Landau-Zener (LZ) model, by employing the nonlinear autoregressive neural network and the long short-term memory neural network. Initially, time-dependent transition probability of the LZ model is obtained by the Dirac-Frenkel time dependent variation with the multiple Davydov $D2$ Ansatz. With the first stage of a two-dimensional (2D) dataset (time versus transition probability), two different kinds of neural networks are trained and validated successfully with sufficient information to predict the future values of transition probability (the second stage) with considerable accuracy. Furthermore, we also develop a framework under which an entire time series of a LZ model with fixed tunneling strength $Δ$ and a given qubit-bath coupling strength $γ$ can be predicted, using neural networks that are trained on a set of pre-generated time series corresponding to various values of $γ$ (3D data: time, $γ$ and transition probability). Considerable accuracy is also achieved in 3D data prediction.

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Hydrogenated C<sub>3</sub>N: Variable-bandgap stable structures and induced antiferromagnetic properties

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Zhenyu Wu, Hong Zhang, Jiahe Lin, Jimin Zhao, Xinlu Cheng

Abstract

C3N, a fully flattened graphene-like structure, has gained a great deal of attention for its excellent performances in electronic and optical characteristics. Inspired by this, we carry out the calculations of hydrogenated C3N structures based on the first-principles theory. We acquire six stable structures from 52 different hydrogenated configurations by the analyses of the absorption energies and phonon dispersions at first. Then, we perform the electronic calculations of the six stable structures, which reveals that the bandgap of C3N can be modulated by hydrogenation. Furthermore, the hydrogenated C3N acquires an induced net magnetic moment in a primitive cell and exhibits an antiferromagnetic ground state. In addition, the structures demonstrate significant characteristics on the absorption spectrum. Our calculations offer an effective way to alter the electronic and optical properties of the 2D materials, and also make contributions to developing novel electronic and spin devices.

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Electronic and thermoelectric properties of RbYSn half-Heusler compound with 8 valence electrons: Spin-orbit coupling effect

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): D.M. Hoat, Mosayeb Naseri

Abstract

In this paper, we present the systematical investigation on the phase stability, electronic structure and thermoelectric properties of new half-Heusler compound RbYSn. The structural and dynamical stabilities of RbYSn are proven. Our calculations show that the studied compound is direct semiconductor with band gap of 0.892 eV. The spin-orbit coupling (SOC) has strong influence on the valence band of RbYSn compound with a split of 0.135 eV at the highest point. Our obtained results show that RbYSn has high thermopower resulting from the favorable features of its band structure. The SOC effect on the thermoelectric properties of RbYSn compound, including Seebeck coefficient, electrical conductivity, electronic thermal conductivity and power factor, also is analyzed and discussed in details. The power factor increases with increasing temperature and its maximum value at 800 K is found between $5.9×1011$ (W/mK2 s) and $6.3×1011$ (W/mK2 s).

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Electron dynamics method using a locally projected group diabatic Fock matrix for molecules and aggregates

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Takehiro Yonehara, Takahito Nakajima

Abstract

We propose a method using reduced size of Hilbert space to describe an electron dynamics in molecule and aggregate based on our previous theoretical scheme (Yonehara and Nakajima, 2017). The real-time time-dependent density functional theory is combined with newly introduced projected group diabatic Fock matrix. First, this projection method is applied to a test donor-acceptor dimer, namely, a naphthalene-tetracyanoethylene with and without initial local excitations and light fields. Secondly, we calculate an absorption spectrum of five-unit-polythiophene monomer. The importance of feedback of instantaneous density to Fock matrix is also clarified. In all cases, half of the orbitals were safely reduced without loss of accuracy in descriptions of properties. The present scheme provides one possible way to investigate and analyze a complex excited electron dynamics in molecular aggregates within a moderate computational cost.

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Spiral waves with interfacial oscillatory chemical reactions emerge in a model of reaction-diffusion systems

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Jian Gao, Changgui Gu, Huijie Yang

Abstract

We propose a model for describing oscillatory chemical reactions involving a variety of immiscible solvents. This model describes the interaction between chemical oscillations on both sides of the interface of different solvents and the effect of the interface on chemical oscillations. Based on this model, we study the spiral chemical wave in a chemical oscillation with interfaces of different solvents, and report a new type of spiral wave. The interface does not hinder the propagation of chemical waves, which can continue to propagate through the interface. The frequency of the chemical wave is increased after the chemical wave passed through the interface. The work of this paper enriched the categories of the dynamics of pattern formation. We believe that the results of this study can provide direction and guidance for chemical experimental research about interfacial oscillatory chemical reactions.

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Measurements and analyses of the conductivities of probe ions in monohydroxy alcohol liquids

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Xing-Yu Zhao, Li-Na Wang, Yu-Fen He, Heng-Wei Zhou, Yi-Neng Huang

Abstract

The conductivities ($σ$) of probe ions in three kinds of monohydroxy alcohol liquids, 2-pentanol, 2-methyl-1-propanol, and 2-methyl-1-pentanol, were measured in the temperature (T) range of 150–375 K. The results show that, with increasing T, $σ$ increases first and then decreases, which is obviously different from the monotonically exponential increase in the typical glass-forming liquid, glycerol. The temperatures (Tσ) corresponding to the maximum $σ$ values are 297, 338, and 300 K, respectively. By comparison with the typical glass-forming liquid, glycerol, it is concluded that Tσ is the crossover temperature between the promotion by thermal activation and the hindrance of the ion motion coming from the interspace reduction among the hydrogen bonding molecular chains due to the decrease of the chain length as T goes up. $σ$ vs $T$ satisfies a phenomenological equation with a modifying factor originating from the hindrance.

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Coherent spin transport in a DNA molecule

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Yukihito Matsuura

Abstract

Coherent spin transport in a DNA molecule has been examined using a first principles calculation. In the calculated model, a B-form double strand (ds) (5′-CGCGAATTCGCG-3′) (Dickerson-Drew duplex) was located between ferromagnetic nickel electrodes and spin transport was calculated under two relative magnetic configurations of electrodes: parallel and antiparallel alignments. As a result, the molecule was too long to demonstrate an efficient coherent spin transport. Short DNA molecules of ds(5′-CGCG-3′) and ds(5′-AATT-3′), which were cut out from the Dickerson-Drew duplex, showed similar results. On the contrary, stacking nucleic acids (π-stacking) of ds(5′-CGCG-3′) or ds(5′-AATT-3′) resulted in an efficient coherent spin transport sufficient to cause spin polarization and a certain difference in conductance by varying the magnetic configuration of ferromagnetic electrodes. This result suggested the possibility of tunnel magnetoresistance in the short π-stacking part of a DNA molecule.

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Molecular dynamics simulation of Couette and Poiseuille Water-Copper nanofluid flows in rough and smooth nanochannels with different roughness configurations

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Davood Toghraie, Maboud Hekmatifar, Yasaman Salehipour, Masoud Afrand

Abstract

In this study, molecular dynamics simulation of Couette and Poiseuille Water-Copper nanofluid flows in rough and smooth nanochannels was performed. The Lennard-Jones equation is considered as Water-Water intermolecular interaction, while Hamaker’s equation is considered to be the interaction between Water-Copper and Copper-Copper particles. PPPM algorithm is used to calculate the electric potential. It is concluded that increasing the channel height reduces the effect of the surface on the fluid and reduces the flow rate of the nanofluid. Also, the slip velocities on the bottom and top walls remain almost the same. Furthermore, nanoparticles have caused fluctuations in the middle area, which are due to the effects of the surface of the nanoparticles relative to the base fluid of the Water. As expected, the presence of nanoparticles in the middle area and the interaction between the surface and the fluid in this area has caused abnormal fluctuations.

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Effect of γ-substituted poly(ɛ-caprolactone) chain length on its coil-to-globule transition temperature in water: A molecular dynamics simulation study

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Amin Koochaki, Mohammad Reza Moghbeli, Sousa Javan Nikkhah

Abstract

The influence of chain length on the coil-to-globule transition temperature (Tcg) of poly{γ-2-[2-(2methoxyethoxy)ethoxy]ethoxy-3-caprolactone} (PMEEECL) chains was investigated via full atomistic molecular dynamics (MD) simulation. Chains with different repeating unit numbers (N) of 5, 10, 15, and 20 were simulated over a wide temperature range. It was found that Tcg increased with increasing N of the PMEEECL chain. The simulation results showed that as the chain contour length is of the order of the Kuhn length, the chain bending and chain collapse become more involved. The chains exhibit significant sensitivity to the temperature when the contour length exceeds the Kuhn length. Nonetheless, for the short chains, i.e. pentamer, the oligomer was temperature insensitive in the studied temperature range. Furthermore, aggregation of five PMEEECL chains with N = 20 was clearly observed at the temperatures above Tcg.

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Assessing the structure of classical molecular optimal control landscapes

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Carlee Joe-Wong, Tak-San Ho, Herschel Rabitz

Abstract

We consider laser-driven optimal control landscape of a molecule from a classical mechanical perspective. The goal of optimal control in the present work is to steer the molecule from an initial state to a target state, denoted by two distinct points in phase space. Thus, a particular control objective is given as the difference between the final achieved phase space point and the target. The corresponding control landscape is defined as the latter control objective as a functional of the control field. While previous examination of the landscape critical points (i.e., a suboptimal point on the landscape where there is a zero gradient) has shown that the landscape topology is generally trap-free, the structure of the landscape away from these critical points is not well understood. We explore the landscape structure by examining an underlying metric defined as the ratio R of the gradient-based optimization path length of the control field evolution to the Euclidean distance between a given initial control field and the resultant optimal control field, where the latter field corresponds to a point at the top of the landscape. We analyze the path length-to-distance ratio R analytically for a linear forced harmonic oscillator and numerically for a nonlinear forced Morse oscillator. For the linear forced harmonic oscillator, we find that $R⩽2$ and reaches its minimum value of 1 (i.e., corresponding to “a straight shot” through control space) in the large target time limit, as well as at special finite target times. The ratio R is similarly small for Morse oscillator simulations when following a steepest-ascent path to the top of the landscape, implying that the landscape is quite smooth and devoid of gnarled features. This conclusion is exemplified for a path discovered with $R≃1.0$ where simply following the initial gradient direction takes the climb very close to the top of the landscape. These findings are consistent with a variety of previous like simulations examining R in quantum control scenarios.

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Post-decorated surface fluorophores enhance the photoluminescence of carbon quantum dots

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Thu-Huyen Thi Dang, Van-Tuan Mai, Quang-Trung Le, Ngoc-Huyen Duong, Xuan-Dung Mai

Abstract

Photoluminescence (PL) is the center property to deploy carbon quantum dots (CQDs) in diverse applications although their physicochemical origin is still debated. Herein, carboxylic-terminated CQDs were synthesized from citric acid (CA) and treated sequentially with ethylenediamine (EDA). Infrared, magnetic, X-ray photoelectron and UV–Vis spectroscopies indicated the formation of surface fluorophores by the EDA treatment. The post-decorated surface fluorophores accounted for a resolved UV absorption band at 346 nm, which originated from HOMO → LUMO transition in the fluorophores. The post-decorated fluorophores dominated the emission spectrum of CQDs when excited with wavelengths below 340 nm and enhanced the PL quantum yield of CQDs from 20.7% to 47.6%. The results pave new understanding on the optical properties of CQDs derived from CA and amines.

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Energy transfer times in fluorographene-based biomimetic light harvesting antennae

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Sayeh Rajabi, Tomáš Mančal

Abstract

It has been demonstrated earlier that graphene-like defects on fluorographene can act as molecules in biomimetic molecular light-harvesting antennae. In competition with radiative and non-radiative losses, transfer time of excitations in an antenna measures its performance. We report on the optimal conditions for excitation energy transfer in artificial antennae built from selected types of fluorographene defects. The excitation transfer dynamics is calculated based on the Frenkel exciton model using hierarchical equations of motion for different values of temperature, system-environment reorganization energy and bath correlation time to study a possible range of parameters pertaining to the fluorographene material. We also study possible energy funnelling in the third dimension for two parallel fluorographene sheets with defects. We conclude that the strength of system-environment interaction is more important for the efficient energy funnelling in our proposed material than a precise control over the structure of artificial antennae.

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First-principles approach to the first step of metal–phosphine bond formation to synthesize alloyed quantum dots using dissimilar metal precursors

Publication date: 1 January 2020

Source: Chemical Physics, Volume 528

Author(s): Junki Nagakubo, Tsutomu Nishihashi, Kenji Mishima, Koichi Yamashita

Abstract

InP-based quantum dots are promising candidates as Cd-free quantum dots; however, they require sharper fluorescence to satisfy the next-generation display standard. For this purpose, a deeper understanding of the crystal growth scheme and well-designed organometallic precursors are needed. Density functional theory calculations were used to find the activation barriers for the initial reaction of Zn, Ga, and In precursors with tris(trimethylsilyl)phosphine, and differences in reactivity between dissimilar metal precursors were revealed. The coordinations of the P precursor to Zn, In, and Ga precursors were found to differ significantly, depending on the coordination number and the ionic radius, and these results were consistent with reports that found that InZnP can be alloyed, but InGaP is not easily alloyed. The activation energies become close to each other when using thiol ligands with less steric hindrance in monodentate ligands. These results will lead to achieving precise composition control and great luminescence properties.

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Effects of the forced convection and current density on the electrodeposition of Zn-Fe-Mo alloys

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Josiel Martins Costa, Mariana Sayuri Hori, Ambrósio Florêncio de Almeida Neto

Abstract

In this study, zinc ternary alloys known for their catalytic application in desulphurization processes were developed by the electrodeposition process. Zn-Fe-Mo ternary alloy was synthesized from an electrolytic bath. The influence of forced convection (9–51 rpm) and current density (1.72–58.28 mA cm−2) on the electrodeposition was evaluated by using a central composite design. It was observed that the decrease in the electric current density resulted in an increase in electrodeposition efficiency from 36 to 68%. According to statistical analysis, the stirring velocity was not significant, however, it was verified that the forced convection phenomenon contributed to increasing the deposition from 30 to 72% for Zn and Fe, and from 37 to 90% for Mo. In addition, the alloys obtained were characterized by X-ray diffraction and scanning electron microscopy (SEM). Diffractograms evidenced the presence of crystalline structures and the SEM micrographs presented coatings with rough and fibrous appearance.

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Spectroscopic and electronic properties of a copolymer and its metal complexes: A theoretical and experimental study

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Aslisah Acikses, Seda Hekim, Fethiye Oksuz

Abstract

A copolymer containing 4-Diethanolaminomethyl Styrene (DEAMSt) monomer with Benzyl Methacrylate (BMA) monomer units were synthesized by free radical solution polymerization technique using AIBN as a free radical initiator and 1,4-dioxane as a solvent at 60 °C. The metal complexes were prepared by reaction of the copolymer used as ligand poly(DEAMSt0.70-co BMA) and Ni(II), Co(II) and Zn(II) metal ions in presence of ethanol and dilute NaOH at 65 °C for 48 h in pH 6. The structure of copolymer used as ligand and polymer-metal complexes were characterized by (FT-IR), 1H NMR, elemental analysis, and SEM-EDX techniques. For the theoretical calculations (FT-IR and 1H NMR spectrum) the Hartree-Fock (HF) theory with 6-31G (6D, 7F) basic set was used. In addition, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energies were investigated. A good agreement has been found between the theoretical and experimental FT-IR and 1H NMR results.

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Synthesis, characterization and spectroscopic studies of surfactant loaded antiulcer drug into Chitosan nanoparticles for interaction with bovine serum albumin

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Mohsen T.A. Qashqoosh, Faiza A.M. Alahdal, Yahiya Kadaf Manea, Syed M. Zakariya, Saeeda Naqvi

Abstract

In the present study, Lansoprazole loaded Chitosan-Tween80 Nanoparticles (NLPZ) have been synthesized by ionotropic gelation method and characterized by FTIR, PXRD, DLS, SEM and UV–Vis techniques. The intermolecular interactions of LPZ and NLPZ with BSA were investigated using fluorescence, UV–vis, circular dichroism, and molecular docking techniques. The spectroscopic techniques suggested effective binding of LPZ and NLPZ to BSA under physiological conditions. The S-V plot of BSA-LPZ system showed positive deviation highlighting the presence of both static and dynamic quenching. Hence, ground state complex model and sphere of action quenching model were used for the study of BSA-LPZ system. The KSV and Ka of BSA-LPZ system were higher as compared to BSA-NLPZ system. Thermodynamic parameters indicated that the binding reaction in both systems was exothermic and spontaneous, enthalpically driven and also hydrogen binding and Van der Waals forces played a major role in the interaction of BSA-LPZ and BSA-NLPZ systems.

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Density Functional Theory modeling of the magnetic susceptibility of heme derivatives

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Abstract

Susceptibility-weighted imaging (SWI) is a magnetic resonance imaging (MRI) technique which magnetic susceptibility differences between tissues can be used as a new type of contrast in MRI. SWI is sensitive to both paramagnetic and diamagnetic substances. Accurate estimations of the magnetic properties of the heme derivatives is essential for the development of the SWI technique.

In this paper, we study structural and magnetic properties of the heme derivatives from Density Functional Theory calculations. By applying the Stoner model we obtained the magnetic susceptibility of the heme derivatives.

We find that the paramagnetic phase of heme, deoxyhemoglobin and aquomethemoglobin to be more stable than the diamagnetic phase as expected from experimentation but the diamagnetic phase of the oxyhemoglobin and hemichrome is more stable. Our results show that the response of the heme to the external magnetic field is changed by the presence of ligand (imidazole or water) molecule.

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Tuning the electronic structure of 2D materials by strain and external electric field: Case of GeI<sub>2</sub> monolayer

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): D.M. Hoat, Tuan V. Vu, Mohammed M. Obeid, Hamad R. Jappor

Abstract

Strain and external electric field effect on electronic structure of GeI2 monolayer has been investigated using first principles calculations. The obtained results indicate that GeI2 monolayer is an indirect semiconductor with band gap value of 2.188 eV. With biaxial strain, the band gap of considered material increases slightly with compression up to −6% and then it decreases and shows abrupt drop for strain −9% to −12%, whereas it just shows decreasing trend with tensile strain. In case of uniaxial strain, the band gap value increases nearly linearly under the effect of considered strain range. The weak external electric field has no significant effect on the band gap of GeI2 monolayer, while with E = $±$0.6 (eV/Å/e), the band gap decreases considerably as I-6s state in conduction band moves to the lower energy levels.

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Influence of Br substituent position at the carbazole on spin-orbit coupling element matrix

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Jing Li, Bo-Ting Yang, Ying Yu, Ye Cao, Xi-Xin Duan, Fan-Ying Meng, Gang Sun, Chun-Guang Liu

Abstract

Based on reported PDCz (1), eight isomers (29) were designed by changing Br substituent positions at the carbazole group to investigate the structure-property relationship by quantum chemistry calculations. The calculated results indicate that an appropriate Br substituent position at the carbazole group is essential for enhancing the spin–orbit coupling (SOC) strength. Among 29, The <S1|HSOC|Tn> (n = 1–5) values of 3 and 7 with Br substituent at 3, 6-position and 1, 3-position are close to those of 1. However, other compounds (2, 46, 8 and 9) have significant increase in SOC values between singlet and triplet excited states. Thus, simply changing the Br substituent position would result in significant SOC variation. The systematical investigation on Br substituent position at the carbazole group would provide valuable information for choosing better Br position in experimental synthesis.

Graphical abstract

Based on PDCz (1), eight regioisomers (29) were designed by changing Br substituent position at the carbazole to investigate the structure and property relationship. The calculated results indicate that simply changing the Br substituent position results in significant spin-orbital coupling (SOC) variation. The <S1|HSOC|Tn> (n = 1–5) values of 3 and 7 with Br substituent at 3, 6-position and 1, 3-position are close to those of 1. The other compounds (2, 46, 8 and 9) have significant increase in SOC between singlet and triplet excited states. On the whole, most compounds containing Br substituent has higher SOC than the one that is not substituted. Moreover, the SOC increase is related to the Br substituent positions on the carbazole group.

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Selective enhancement of single-order and two-order harmonics from He atom via two-color and three-color laser fields

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Yi Li, Liqiang Feng, Yan Qiao

Abstract

An effective method to achieve the selective enhancement of single-order and two-order harmonics from He atom has been proposed through laser waveform control of two-color and three-color laser fields. Firstly, with the optimization of ω-2ω two-color laser waveform, not only the wavelength tunable single-order harmonic (i.e. from 182th order to 328th order) can be enhanced by 17 times compared with the neighbor harmonics, but also the enhancement of two-order harmonics can also be obtained. Theoretical analyses show that the enhancement of the specific harmonics is coming from the folded structure on the short quantum path of the harmonic emission peak. Detail analyses show that the above folded structure happens in the reversed sub-peak region of the half-cycle laser waveform, where the deceleration and further acceleration of the free electron can be found in this structure. Moreover, this structure is dependent on the pulse duration of the controlling pulse. However, it is not very sensitive to the wavelength of the controlling pulse. Further, by properly adding a 3ω pulse, not only the efficiency of spectral continuum can be enhanced by 300 times compared with that from the two-color field, but also the generation of single-order harmonic with the intensity enhancement of 20 times can be found. Furthermore, the enhancement of the harmonic spectrum can also be achieved when using the 4ω or 6ω controlling pulses.

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Exploring the opto-electronic and charge transfer nature of <em>F</em>-BODIPY derivatives at molecular level: A theoretical perspective

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Aijaz Rasool Chaudhry, Shabbir Muhammad, Bakhtiar Ul Haq, A. Laref, A. Shaari, Mazhar Amjad Gilani

Abstract

The goal of current work is to investigate the effect of ethyl group on the electronic, photo-physical and charge transport properties of F-BODIPY, which has been explored at the molecular level after substituting ethyl group at two position of F-BODIPY molecule. In current study; optical, electronic and charge transfer properties for F-BODIPY derivatives (Comp_1, Comp_2 and Comp_3) have been theoretically investigated. All the molecules have been optimized at the ground (S0) and first excited (S1) states using density functional theory (DFT) and time dependent DFT (TD- DFT) with the hybrid functional/basis set (B3LYP /6-31G**), respectively. Effect of ethyl groups at two different positions on the electronic, optical and charge transport properties of 5,5-difluoro-1,37,9-tetramethyloctahydro-1H,5H-514-dipyrrolo[1,2-c:2′,1′-f] [1–3] diazaborinine (Comp_1) as parent molecule has been studied at molecular level. The introduction of ethyl at two positions in Comp_1 led to a red shifted absorption spectra in comparison with parent molecule in the violet region. Various properties of interest such as highest occupied molecular orbitals (HOMO), lowest unoccupied molecular orbitals (LUMO), vertical electron affinity (EAv), adiabatic electron affinity (EAa), vertical ionization potential (IPv), adiabatic ionization potential (IPa), electron reorganization energies (λe) and hole reorganization energies (λh) were explored. Additionally, global reactivity descriptors e.g. electronic chemical potential (μ), electronegativity (χ), Electrophilicity (ω), hardness (η), softness (S) and electrophilicity index (ωi) have been calculated theoretically.

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The light-harvesting complex 2 of <em>Allochromatium vinosum</em>: B800 absorption band splitting and exciton relaxation

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Xiaomeng Liu, Oliver Kühn

Abstract

Allochromatium (Alc.) vinosum has a double-peak structure of its absorption band around 800 nm. Previously, the excitonic origin of this feature has been demonstrated experimentally, but a detailed understanding still lacks a model Hamiltonian being able to reproduce absorption as well as exciton relaxation time scales. Here, we propose a system-bath model which accommodates these observables. It combines Frenkel exciton theory for a dimerized and energetically heterogeneous B800 pigment pool with a quantum master equation approach describing phase and energy relaxation according to an experimental spectral density. The analysis of this model shows that the LH2 of Alc. vinosum features an interesting interplay of two excitonic bands, which are originating from the different pigment pools.

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Macroscopic simulation of nanofluid turbulent flow due to compound turbulator in a pipe

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Qingang Xiong, M. Jafaryar, Alireza Divsalar, M. Sheikholeslami, Ahmad Shafee, Dat D. Vo, Muhammad Humran Khan, I. Tlili, Zhixiong Li

Abstract

A numerical analysis of Copper oxide-H2O nanomaterial hydrothermal characteristics through a duct with utilizing turbulator under constant heat flux has been carried out by means of FVM. Simulations contain the effect of width tape (b) and Reynolds number (Re). Single phase model for nanomaterial and k-ɛ for turbulence modeling have been selected. Outputs indicate that friction factor tends to decline with augment of Re. Greater Nu due to insertion of turbulator is related to swirl flow generation. Augmented convective heat transfer is obtained with inserting turbulator with higher width.

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Thermodynamic study of interactions between 1-alkanol and butanone

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Abstract

To obtain the new perspectives on the molecular interactions in the binary systems of butanone and a homologous series of 1-alkanol from 1-pentanol up to 1-decanol, these mixtures were studied using the Kirkwood–Buff (KB) formalism and preferential solvation analysis. The results were confirmed using the experimental excess molar volumes. KB integrals$Gij$, the excess or deficit number$Δnij$, and solvation coefficients $δij$are reported here. Analysis of obtained data regarding the KB formalism and preferential solvation reveals that interactions strength in mixtures depends on the butanone concentration and size of 1-alkanol. Also, interactions between similar molecules are remarkable and become stronger as the length of the alcohol increases. Furthermore, mixtures structure was studied using the concentration-concentration structure factor, $SCC(0)$. Results from application of this parameter show that the homocoordination occurs in solutions. Steric effects lead to the stronger orientations in the mentioned mixtures.

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Physico-chemical investigation of catalytic oxidation sites in 4%Rh/CeO<sub>2</sub> catalysts prepared by impregnation and deposition–precipitation methods

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Abstract

4 wt% Rh/CeO2 catalysts were prepared by two different methods: deposition–precipitation (DP) and impregnation (Imp). X-ray diffraction (XRD), differential scanning calorimetry and thermogravimetry (DSC-TG), temperature-programmed reduction (TPR), and electron paramagnetic resonance (EPR) were used for physicochemical characterization. The solids were tested in propylene and carbon black oxidation reactions. The 4%Rh/CeO2 (DP) showed better catalytic performance in both reactions compared to the catalyst prepared by the impregnation method. The XRD technique evidenced the formation of Rh2O3 phase in the DP-solid after calcination of this latter at 400 °C for 4 h. EPR evidenced, only in the DP-solid, the presence of O2 species in interaction with the CeO2 surface whereas Rh4+ ions in the form of clusters were identified in both solids. The TPR technique showed that the DP-solid was reduced by hydrogen at lower temperature compared to the impregnated one. The higher catalytic performance of the DP-solid was attributed to the presence of O2 species along with the presence of Rh2O3 phase in ceria and to the better reducibility and lower particle size of the rhodium species.

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Simulations of pump probe spectra of a molecular complex at high excitation intensity

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Vytautas Bubilaitis, Jürgen Hauer, Darius Abramavicius

Abstract

The most wide spread theoretical treatment of molecular non-linear spectroscopy and quantum dynamical processes employs a perturbative expansion in powers of the excitation field. However, its direct application requires knowing multi-excitonic state energies and their relaxation pathways. This is not necessary if real space propagation is used. In this paper, the standard Nonlinear Exciton Equations (NEE) for molecular excitations are extended to include fifth order processes. The coherent part of it corresponds to saturation of molecular transition dipoles, while the incoherent part is constructed to reflect the exciton-exciton annihilation (EEA) processes. We show that numerical NEE-based simulations of pump probe spectra of a molecular dimer quantitatively describe both coherent and incoherent processes as a function of excitation intensity.

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A new acetal as a fluorescent probe for highly selective detection of Fe<sup>3+</sup> and its application in bioimaging

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Min Wang, Yong-Ming Zhang, Qin-Yi Zhao, Zhen-Hai Fu, Zhi-Hong Zhang

Abstract

A simple fluorescent probe L for Fe3+ was easily synthesized based on anthracene. Among the various metal ions including Fe2+, this probe exhibited high sensitivity and good selectivity toward Fe3+ with turn-off fluorescence mode in DMSO-HEPES buffer solution (20 mM, pH = 7.0, 1:1 (v/v)). When adequate Fe3+ ion was added into the solution of probe L, its molecular structure transferred from anthraldehyde dimethyl acetal to anthraldehyde, resulting in fluorescence quenching with a low detection limit of 3.08 μM. 1H NMR spectra and TLC analysis further supported this concept. Finally, this probe was successfully applied in bioimaging.

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On the hydrophobic effect in water–alcohol mixtures

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Javier Catalán, Cristina Díaz-Oliva, Francisco García-Blanco

Abstract

Binary mixtures of water and various alcohols (W/ROH) were characterized in the light of the pure solvent scales, using suitable probe/homomorph couples. Various thermodynamic properties (viz. vapour pressure and enthalpy of mixing), viscosity, and the IR and NMR spectroscopic properties of the mixtures, as well as the solvatochromic behaviour on UV [NA, ENB, ET(30), and Z] and NMR probes (124Xe) are described in terms of microscopic properties like polarity, acidity, and basicity, and the descriptions examined in relation to a potential physical significance. Finally, the hydrophobic effect is discussed in the light of the results.

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Theoretical analysis of the stabilization of graphene nanosheets by means of strongly polarized pyrene derivatives

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Nadeesha J. Silva, Itamar Borges, Patrick A. Tone, Micah J. Green, Hans Lischka, Adelia J.A. Aquino

Abstract

Functionalized pyrenes have been used in experimental work as dispersants to avoid the re-association of graphene sheets in order to produce single (few) layer graphene sheets. In the present studies, the adsorption processes of various pyrene derivatives on a planar model graphene layer were studied theoretically to determine the influence of different polar pyrene substituents on the strength of their interaction with graphene. Based on the previous experimental work, the following substituted pyrenes were investigated: pyrene butanol, pyrene sulfonic acid, neutral, charged or with counter ion, and pyrene tetra-sulfonic acid, either negatively charged or neutral. The calculations were based on density functional theory and the effects of the solvents water and ethanol were included via a continuum approach and explicit solvent interactions. The results show that the number of polar substituents is a decisive factor for stabilization of the pyrenes on the graphene surface.

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Studying the spectral diffusion dynamics of chlorophyll <em>a</em> and chlorophyll <em>b</em> using two-dimensional electronic spectroscopy

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): M. Faisal Khyasudeen, Paweł J. Nowakowski, Hoang Long Nguyen, Jamie H.N. Sim, Thanh Nhut Do, Howe-Siang Tan

Abstract

Chlorophyll a (Chl a) and Chlorophyll b (Chl b) are major pigments in the photosynthetic machinery in green plants. Despite their similarities in chemical structures, the relaxation dynamics as observed in the ultrafast methods, such as pump probe and multidimensional spectroscopy, demonstrate a distinct kinetics. Here, we employ the ultrafast two-dimensional electronic spectroscopy (2DES) method to characterize the frequency fluctuation correlation function (FFCF) for Chl a and Chl b in various solvent environments, through the Centre Line Slope (CLS) method. We observe that the FFCF decay for both Chl a and Chl b in the methanol solvent environment has a ~40 ps component that is absent in aprotic solvents, tetrahydrofuran and diethyl ether. We observe also that Chl b exhibit higher values of inhomogeneous broadening than Chl a.

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Many unknowns below or close to the experimentally known cumulene carbene – A case study of C<sub>9</sub>H<sub>2</sub> isomers

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Krishnan Thirumoorthy, Mayavan Viji, Aditya P. Pandey, Tanmay G. Netke, Baranitharan Sekar, Garima Yadav, Saurabh Deshpande, Venkatesan S. Thimmakondu

Abstract

Twenty-five low-lying isomers of C9H2 lying within 2 eV (∼46.12 kcal mol−1) have been theoretically investigated using high-level quantum chemical calculations. Among them, the linear triplet isomer (1), the cyclopropenylidene derivatives (2 and 3) and the cumulene carbene isomer (11) have already been detected in the laboratory. The present theoretical study proposes fourteen cyclic structures and four open-chain structures that have not been investigated before. On the basis of relative energies obtained from coupled-cluster calculations, the current theoretical study reveals that six isomers (4 and 610), which energetically lie below 11, and fourteen isomers (1225), which energetically lie above 11, are remaining elusive in the laboratory to date. Considering the astronomical importance of cyclopropenylidene and cumulene carbenes, the current quantum chemical data may be of relevance to molecular spectroscopists in identifying new C9H2 isomers in the laboratory. Consequently, such studies may benefit radioastronomers in confirming or neglecting C9H2 isomers in the interstellar medium.

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Preparation of perovskite microfibers by lead bromide self-assembly in aqueous solution assisted methylamine bromide vapor deposition

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Wei-Long Xu, Weibai Bian, Hai-Yue Chen, Min Zheng, Chao Xiong, Xiao-Yan Jiang, Lan-Hua Dai

Abstract

One-dimensional perovskites have potential applications in solar cells, lasers, photodetectors and optical waveguides. In this work, lead bromide microfibers which were prepared by self-assembly effect in aqueous solution. Perovskite microfibers were synthesized by using lead bromide microfibers as templates in the vapor atmosphere of methylamine bromide. The perovskite phase of microfibers was verified by the X-ray diffraction and photoluminescence spectrum. The higher trap density at the boundaries compared with the bulk regions of the microfibers, leading to the shorter fluorescence lifetime, which was observed by the combination of spatially and temporally resolved fluorescence measurement.

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Electric polarization of electron-hole pairs in organic semiconductors induced by picosecond pulses of an electromagnetic wave: Consideration of small-molecule semiconductors with a negligibly small concentration of traps

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): L.V. Lukin

Abstract

Non-stationary conductivity of an organic semiconductor is discussed for the conditions of the time-resolved pump-probe experiments, in which electrons and holes are produced by the pump femtosecond laser pulse followed by the action of the terahertz (THz) probe pulse with duration of the order of 1 ps. The developed diffusion model is applicable to small-molecule semiconductors without traps. The time dependence of conductivity due to polarization of electron-holes pairs by the electric field of the THz pulse is found as a function of the sum of the electron-hole mobilities and delay time between the pump and probe pulses.

Graphical abstract

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Melting suspending of Ag nano-particles monitored by molecular dynamics simulation

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): Xin Wang, Xueliang Wang, Miao Liu, Yaping Wang

Abstract

Melting suspending, defined as the incomplete melting of the nano-particles (NPs), was found by the molecular dynamics (MD) simulation with the embedded atom method (EAM) force field. The suspending of isolated Ag NPs occurs while the melting layer reached a given thickness around the solid core below a critical temperature, and the thickness of liquid layer is mainly dependent on the holding temperature rather than the holding time. Above the critical temperature, complete melting of the whole NPs occurs spontaneously at temperatures below the thermodynamic equilibrium melting point (Tem). It also should be noted that the critical temperature is size dependent and is independent from the atom configuration of the surface particles.

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Electronic circular dichroism with real time time dependent density functional theory: Propagator formalism and gauge dependence

Publication date: 1 November 2019

Source: Chemical Physics, Volume 527

Author(s): J. Mattiat, S. Luber

Abstract

Linear response theory is reviewed in a propagator formalism to treat linear response and real time (RT) time dependent density functional theory (TDDFT) in a common framework for the calculation of linear response tensors. The importance of an additional term in the definition of the momentum for a description in the velocity representation as well as an origin independent linear magnetic response in the presence of non-local pseudo potentials is discussed. The origin and meaning of the terms ‘representation’ and ‘gauge’ are explored and simulations of absorption and electronic circular dichroism spectra using RT-TDDFT are presented. The calculation of the electro-magnetic linear response functions has been implemented into the package `CP2K` using the gaussian and (augmented) plane wave method.

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Electrochemically active water repelling perfluorinated polyaniline films

Publication date: Available online 21 September 2019

Source: Chemical Physics

Author(s): Panagiotis Dallas, Elena Tomšík, Ruth Sang Jones, Albert Xiao, Eleanor Milnes-Smith, Nicole Grobert, Kyriakos Porfyrakis

Abstract

Water repelling, perfluorinated, polyanilines and their composites with multi-wall carbon nanotubes are synthesized using interfacial polymerization in either flake-like or fibrillar shapes. This class of polyanilines exhibits electrochemical activity, capacitive behaviour, and a contact angle of 119-125o with water. The addition of multi-wall carbon nanotubes facilitates the control of the polymer morphology and increases the specific capacitance of the material. We obtained microfibers or flake-like morphologies depending on the amount of multi-wall carbon nanotubes added in the organic phase and through cyclic voltammetry, impedance spectroscopy and galvanostatic charge-discharge, we evaluated the effect of the backbone geometry and the addition of nanotubes on the electrochemical properties of the composites and the pristine polymers. The capacitance of the linear 3-perfluoroctyl polyaniline is consistently better than the cross-linked 4-perfluoroctyl polyaniline, where the para position relative to the amine group is blocked by fluorocarbon chains.

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Entner-Doudoroff glycolysis pathway as quadratic-cubic mixed autocatalytic network: A kinetic assay

Publication date: Available online 19 September 2019

Source: Chemical Physics

Author(s): Sharmistha Dhatt, Shrabani Sen, Pinaki Chaudhury

Abstract

Concentration oscillations are ubiquitous phenomenon in biochemical systems.

The present paper considers the simple nonlinear chemical feedback model for standard glycolytic route with prototype autocatalytic steps

Cubic S+2P ⇄ 3P

We couple these steps to get the mixed quadratic –cubic model but remarkable array of complex behavior and oscillatory patterns as expected on coupling is surprisingly missing. The observation is in conformity with natural glycolytic alternatives like the Entner–Doudoroff (ED), and phosphoketolase pathways found in Archaea – Thermoproteustenax and other prokaryotes. The fundamental and the practical implications of our findings are thoroughly discussed with pilot calculations and numerical simulations supported via non-linear dynamic analysis. A basic kinetic scheme is suggested for natural glycolytic alternative, ED pathway with its comparison and contrast to other standard routes for glucose metabolism. A key outcome of the study is the phenomenon of oscillator death for the coupled network. A discussion on the thermodynamic aspect of entropy production rate for the model networks are also presented for a comparison.

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Theoretical prediction of two-dimensional ZnO/GaN van der Waals heterostructure as a photocatalyst for water splitting

Publication date: Available online 19 September 2019

Source: Chemical Physics

Author(s): Kai Ren, Yi Luo, Jin Yu, Wencheng Tang

Abstract

In this work, based on density functional calculations, the structural, electronic, interfacial and optical performances of the two-dimensional van der Waals (vdW) heterostructure formed by ZnO and GaN are addressed. The heterostructure possesses a type-II band structure and decent band edge positions which can separate the photogenerated electron–holes pairs constantly for redox reaction of the water splitting at pH 0 and 7. The charge-density difference and potential drop across the interface of the heterostructure are investigated, which can result a built-in electric field to prevent the recombination of the photogenerated electron–holes. Besides, the high mobility of electrons about 3004.49 cm2·V–1·s–1 is found in the heterostructure along the transport direction. The heterostructure also has excellent optical absorption performance, which can be mediated by the external strain. This study offers guidelines for the design of vdW heterostructures used as photocatalysts for water splitting.

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Effect of fluorine substitution on photovoltaic properties of benzotriazole polymers

Publication date: Available online 17 September 2019

Source: Chemical Physics

Author(s): Hao Chang, Ling Li, Can Zhu, Hongjian Peng, Yingping Zou

Abstract

Two kinds of wide bandgap conjugated polymers, named as BDT-TTBTA and BDT-TTFBTA, were designed and synthesized based on alkylthiophene-modified benzo[1,2-b:4,5-b’]dithiophene (BDT) as the donor unit, benzotriazole (BTA) / fluorobenzotriazole (FBTA) as acceptor units and alkylthiophenothiophene as π-bridge. The thermal stability, absorption spectra, electrochemical properties and active layer morphology of these polymers were investigated to explore the impacts of F atoms on the photovoltaic performance of polymer. By introducing F atom, BDT-TTFBTA:ITIC devices obtained higher open circuit voltage (Voc) of 0.75eV, fill factor (FF) of 48%, and short-circuit current (Jsc) of 12.39 mA·cm-2 than BDT-TTBTA:ITIC devices, giving rise to a higher power conversion efficiency (PCE) of 4.5% compare to BDT-TTBTA:ITIC devices.

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Comparison of methods to study excitation energy transfer in molecular multichromophoric systems

Publication date: Available online 26 August 2019

Source: Chemical Physics

Author(s): Anna S. Bondarenko, Jasper Knoester, Thomas L.C. Jansen

Abstract

We compare theoretical methods for calculating excitation energy transfer rates in multichromophoric systems. The employed methods are the multichromophoric Förster resonance energy transfer (MC-FRET), the numerical integration of the Schrödinger equation (NISE), and the Haken-Strobl-Reineker (HSR) model. As a reference, we use the numerically exact Hierarchy of Equations of Motion (HEOM). We examine these methods in various system and bath parameter regimes including the regime relevant to biological light-harvesting systems. We apply them to a model system of a monomeric donor coupled to a multichromophoric acceptor ring of varying size in two limiting configurations, namely symmetric and asymmetric. We find that the symmetric case is more sensitive to the approximations of the methods studied. The NISE method gives the most reasonable results throughout the parameter regimes tested, while still being computationally tractable.

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Understanding ferromagnetism in Ni-doped MoS<sub>2</sub> monolayer from first principles

Publication date: Available online 19 August 2019

Source: Chemical Physics

Author(s): Xiaoping Han, Maamar Benkraouda, Naser Qamhieh, Noureddine Amrane

Abstract

The electronic and magnetic properties of Ni-doped MoS2 monolayer have been investigated using the DFT+U method. Two kinds of dopants are considered in the 6×6 supercells of MoS2 monolayer: one Ni substitution for Mo, and two Ni substitutions. Results show that both dopants induce ferromagnetism in MoS2 monolayer. With a single Ni dopant, the Ni-induced spins on the nearby host atoms are parallel to that on Ni atom through the p-d hybridization, leading to the ferromagnetic (FM) ordering. Two Ni substitutions energetically prefer to cluster together, which makes the FM coupling in the system include (1) the FM p-d hybridization between Ni and neighboring host atoms, and (2) the FM ordering between two Ni atoms due to the Ni(3d)-S(3p)-Ni(3d) superexchange. Efforts have been done to elaborate the favorability for incorporating Ni dopants in MoS2 monolayer. This work has implications for improving the applications of MoS2 to spintronic even magneto-optic devices.

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Generalized Huang-Rhys factors for molecular aggregates

Publication date: Available online 17 August 2019

Source: Chemical Physics

Author(s): Maxim F. Gelin, Lipeng Chen, Raffaele Borrelli, Erling Thyrhaug

Abstract

Stimulated Raman spectra of molecular aggregates are often remarkably dissimilar to other vibrational spectra e.g. resonance Raman and hole-burning. Particularly in photosynthetic proteins, extremely sparse and predominantly low-frequency spectra are common, unlike the rich structure typical in spectra obtained by frequency-domain techniques. Thus, a mechanism which selectively enhances the intensity of only a small subset of vibronic transitions under stimulated Raman conditions in molecular complexes seems to be required. In this work, we explore how pigment-localized vibrations couple to the excitonic states of molecular aggregates – and the consequences for spectral observables. To aid in the analysis we introduce the concept of a generalized Huang-Rhys factor for molecular aggregates, we derive an analytical expression for this quantity, and established two conditions required for strong vibronic coupling. We illustrate the effect of such coupling by simulation of absorption and resonance Raman spectra of a two-mode model dimer.

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Theoretical Calculations of <sup>1</sup>H NMR Chemical Shifts for Nitrogenated Compounds in Chloroform Solution

Publication date: Available online 12 August 2019

Source: Chemical Physics

Author(s): Haroldo C. Da Silva, Wagner B. De Almeida

Abstract

In this work we report DFT and MP2 1H NMR calculations using the GIAO method and TMS as reference, for a series of nitrogenated compounds in chloroform solution to assess the ability of available theoretical models to reproduce experimental 1H NMR spectra measured in CDCl3 solution, focusing on CHn and N-H proton signals which are relevant in conformational analysis studies. The Polarizable Continuum Model (PCM) may not work successfully to predict N-H chemical shifts in solution. Only when a few explicit solvent molecules are used in DFT-PCM-CHCl3 geometry optimizations a good agreement with experimental N-H chemical shifts measured in solution is reached, indicating that this is a reliable computational procedure for the prediction of the full NMR spectra of organic molecules containing N-H group. However, finding adequate DFT optimized solvated solute structures which reproduce well both N-H and CHn proton NMR signals can become a hard-computational task

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Inclusion of explicit solvent molecules (n = 1, 2, 3, 4) in DFT-PCM-CHCl3 calculations of 1H NMR chemical shifts for the amine compound valerolactam, serves as good example of great improvement of theoretical NMR predictions, concerning N-H protons, which are systematically underestimated using the PCM solvent model, with the difference between theoretical and experimental values in solution approaching acceptable values (CH2 = 0.1 ppm, N-H = -0.2 ppm) when four explicit solvent molecules are included (PCM+4CHCl3 model).

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Understanding the Coalescence and Non-Coalescence of Underwater Oil Droplets

Publication date: Available online 26 July 2019

Source: Chemical Physics

Author(s): Shuai Chen, Jiadao Wang, Chaolang Chen, Awais Mahmood

Abstract

Oil collection requires effective methods to accelerate coalescence of oil in water. The coalescence behaviors of n-hexane, n-heptane, n-octane, dichloromethane and carbon tetrachloride droplets on oleophobic surfaces in water are investigated by experiments and simulations. Experimental results show that the n-hexane, n-heptane and n-octane droplets coalesce in water while the dichloromethane and carbon tetrachloride droplets do not coalesce. Theoretical calculations indicate that the critical thickness of water film between oil droplets to rupture in experiment is several nanometers, which is exactly in the size scale of molecular dynamics simulation. To investigate the mechanisms underlying the coalescence/non-coalescence, molecular dynamics simulations on the oil/water/oil interface are carried out. The simulation results indicate that the orientated oil molecules and increased number of hydrogen bonds in water are main reasons why oil/water/oil interface is stable. To undermine the stability, oleophilic surface in water is constructed, resulting in the coalescence of carbon tetrachloride droplets.

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The effects of TMDD-PA concentration on roughness of Si &#60;110> and etching rate ratio of Si &#60;110>/&#60;111> in alkaline KOH solution

Publication date: Available online 5 June 2019

Source: Chemical Physics

Author(s): Chunlin Zhu, Qingbin Jiao, Xin Tan, Hao Hu, Bayanheshig

Abstract

High aspect ratio gratings (HARG) can be obtained by anisotropic etching of Si <110>/<111>. Usually isopropyl alcohol (IPA) is added to the solution in order to smooth Si <110> surface. However, the addition of IPA can reduce the etching rate ratio of Si <110>/<111>, which leads to a reduction of grating’s aspect ratio. The effects of another additive TMDD-PA (TMDD: IPA = 1: 1 in wt%) were discussed. The experimental data indicates that TMDD-PA behaves better than IPA when smoothing Si <110> surface, and etching rate ratio of Si <110>/<111> increases with the increasing concentration of TMDD-PA. Mechanism of IPA and TMDD-PA in etching were analyzed. Molecules of IPA and TMDD behave differently on Si surfaces, and they have different impacts on H2O molecules.

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Category: Current Chemistry Research

Last update: 28.03.2018.