# Chemical Physics

## Current research reports and chronological list of recent articles.

The international scientific journal Chemical Physics welcomes experimental and theoretical papers in the molecular, biological and materials sciences.

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## Chemical Physics - Abstracts

Effects of adding LiBF4 on the glass-transition kinetics of 1,2-propanediol

Publication date: Available online 20 September 2017
Source:Chemical Physics

Author(s): Yukio Terashima, Kiyoshi Takeda

By applying an isoconversional method to differential-scanning calorimetry (DSC) data, we have discovered that the addition of LiBF4 significantly affects the activation energy Eα of the glass transition of 1,2-propanediol. Depending upon its concentration, the dynamics of the glass transition are affected more by adding LiBF4 at an early stage of the glass-to-liquid transition rather than at later stages. As the mole fraction x of LiBF4 increases, the value of Eα initially increases, but it decreases dramatically during the glass transition. The abrupt decline in Eα suggests that the addition of LiBF4 breaks cooperative rearranging motions into smaller parts. The expansion of cooperativity, and its fragmentation with increasing temperature, can be explained in terms of competition between the hydrogen-bond networks of the alcohol solvent and the ionic interactions due to the added salt. The variability of Eα with temperature is found to correlate exponentially with the dynamic fragility.

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Datum: 24.09.2017

A statistical mechanics investigation about general aspects of wetting transition occurring in nonpolar neutral molecule system with a smooth solid wall

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Shiqi Zhou

Classical density functional theory is used to study the general aspects of wetting phenomena occurring in nonpolar neutral molecule system near a flat solid wall. Current cognitions of the wetting behavior are looked at, validated, corrected and extended. Several new observations are made: (i) the present theoretical calculations suggest that over a broad range of the surface potential parameters the pre-wetting transition temperature interval significantly reduces with the wetting temperature, and at the same time a continuous and monotonous increase of the wetting temperature is induced by decreasing the surface potential range and/or relative strength of surface atom versus fluid atom interaction. (ii) There exist lower limit values of both the surface potential range and the relative strength, below which the wetting transition is impossible. (iv) The present theoretical calculations confirm an experimentally found no adsorption occurring in weak surface potential substrates all the way to the relevant critical temperature by showing the impossibility of wetting at bulk critical temperature and its surroundings; moreover, the calculations extend the experimental observation to a wider parameter domain by indicating that the impossibility is not only unique feature of the weak surface potential substrates, but also applies to all situations of the surface potential range and relative strength. (v) With progressive increase of the relative strength and/or progressive decrease of the temperature, the interfacial phase behavior becomes increasingly complex: the (pre-)wetting transition and layering transition (which can be thermodynamically stable, metastable or even situated at supersaturated vapor phase) are intertwined closely; this challenges the popular knowledge that there is no (pre-)wetting for strong substrates for which the pre-wetting is replaced by the layering transitions.

Datum: 24.09.2017

Van der Waals potential and vibrational energy levels of the ground state radon dimer

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Xiaowei Sheng, Shifeng Qian, Fengfei Hu

In the present paper, the ground state van der Waals potential of the Radon dimer is described by the Tang-Toennies potential model, which requires five essential parameters. Among them, the two dispersion coefficients $C 6$ and $C 8$ are estimated from the well determined dispersion coefficients $C 6$ and $C 8$ of Xe2. $C 10$ is estimated by using the approximation equation that $C 6 C 10 / C 8 2$ has an average value of 1.221 for all the rare gas dimers. With these estimated dispersion coefficients and the well determined well depth $D e$ and $R e$ the Born–Mayer parameters $A$ and $b$ are derived. Then the vibrational energy levels of the ground state radon dimer are calculated. 40 vibrational energy levels are observed in the ground state of Rn2 dimer. The last vibrational energy level is bound by only 0.0012cm−1.

Datum: 24.09.2017

Contents

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Datum: 24.09.2017

IR induced photochemistry of glycolaldehyde in nitrogen matrix

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Author(s): Fabrice Duvernay, Teddy Butscher, Thierry Chiavassa, Stephane Coussan

The conformational equilibria and IR isomerisation processes of glycolaldehyde (HOCH2CHO) conformers have been studied at low temperature in nitrogen cryogenic matrix. The effects of selective IR irradiation, in the $ν OH$ and $ν CH$ domains, have been followed by FTIR spectroscopy. After deposition the main form is the most stable one, CC (Cis-Cis), which features an intramolecular hydrogen bond. Upon selective IR irradiation, this latter form is able to interconvert into two open forms, those called TT (Trans–Trans), and TG (Trans-Gauche). From TT and TG forms, no recovering (by tunneling, dark process, irradiation, annealing, etc.) of the initial state (i.e. CC regeneration) has been observed. However, a TTTG thermal equilibrium is observed with a standard reaction enthalpy about 0.37kJmol−1.

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Datum: 24.09.2017

The Effect of Site-Specific Spectral Densities on the High-Dimensional Exciton-Vibrational Dynamics in the FMO Complex

Publication date: Available online 23 September 2017
Source:Chemical Physics

Author(s): Jan Schulze, Mohamed F. Shibl, Mohammed J. Al-Marri, Oliver Kühn

The coupled exciton-vibrational dynamics of a three-site model of the FMO complex is investigated using the Multi-layer Multi-configuration Time-dependent Hartree (ML-MCTDH) approach. Emphasis is put on the effect of the spectral density on the exciton state populations as well as on the vibrational and vibronic non-equilibrium excitations. Models which use either a single or site-specific spectral densities are contrasted to a spectral density adapted from experiment. For the transfer efficiency, the total integrated Huang-Rhys factor is found to be more important than details of the spectral distributions. However, the latter are relevant for the obtained non-equilibrium vibrational and vibronic distributions and thus influence the actual pattern of population relaxation.

Datum: 24.09.2017

Time-resolved photoelectron signals from bifurcating electron wavepackets propagated across conical intersection in path-branching dynamics

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Yasuki Arasaki, Kazuo Takatsuka

A computational scheme of energy- and geometry-dependent photoelectron signals from the dynamics near a conical intersection based on a simplified path-branching representation of nonadiabatic electron wavepacket dynamics is proposed. Taking the NO2 $X / A$ conical intersection as an example, the results of the present scheme compared to those from previous study based on the method of full quantum vibrational wavepacket shows qualitative agreement suggesting promising application to computation in larger systems intractable to full quantum exact methods.

Datum: 24.09.2017

The effect of varied pH on the luminescence characteristics of antibody–mercaptoacetic acid conjugated ZnS nanowires

Publication date: Available online 8 September 2017
Source:Chemical Physics

Author(s): Madeeha Chaudhry, Malik Abdul Rehman, Asghari Gul, Raheel Qamar, Arshad Saleem Bhatti

We demonstrate here that the effect of varied pH of the media on the photoluminescence (PL) properties of mercaptoacetic acid (MAA) and digoxin antibody (Ab) conjugated zinc sulphide (ZnS) nanowires. The charge-transfer kinetics from MAA to ZnS and vice versa showed a profound effect on the luminescence of ZnS defect states. The PL intensity of the ZnS defect states showed strong dependence on the value of pH with respect to the pKa of MAA. The carboxyl and thiol group of MAA in the protonated (pH&lt;pKa) and deprotonated (pH&gt;pKa) states resulted in the quenched PL intensity. While for pHpKa, the PL intensity was regained as there was equal probability of both protonated and deprotonated carboxyl and thiol groups. These findings indicated that pH of the environment is a key parameter for the use of MAA-Ab conjugated ZnS nanowires as an optical biomarker.

Datum: 24.09.2017

First-principles investigation of decomposition and adsorption properties of RDX on the surface of MgH2

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Author(s): Guo-Ning Rao, Miao Yao, Jin-Hua Peng

Surface adsorption and decomposition mechanisms of cyclotrimethylenetrinitramine (RDX) molecules on the MgH2 (110) crystal face are investigated in this paper by employing the First-Principles. With the N-NO2 bond of RDX molecules asa reference, 12 adsorption sites are considered that are vertical (V1-V6) and parallel (P1-P6) to the MgH2 (110) surface. Results show that these 12 types of adsorption of RDX molecules on the MgH2 (110) crystal face are all chemical adsorption with high heat release, where the vertical Mg-top position (V1) is the most stable adsorption configuration. In all the 12 types of chemical adsorption, RDX molecules are decomposed, through 4 mechanisms including bis-nitro mono-N-O bond rupture, mono-nitro mono-N-O bond rupture, mono-nitro bis-N-O bond rupture and mono-N-O2 bond rupture, where the V-type adsorption is due to N-O bond rupture and the P-type adsorption is due to N-NO2 bond rupture, resulting in RDX decomposition. Secondly, in proximity to the Fermi level, the density of states of the RDX molecule highly coincides with that of the MgH2 (110) crystal face, which is prone to cause orbital hybridization and RDX decomposition. Also, the density of states in proximity to the Fermi level is mainly contributed by nitro O atoms and ring N atoms of RDX, as well asMg atoms of the MgH2 (110) crystal face, and these 3 types of atoms are also active centers for chemical adsorption and decomposition reaction. Finally, an obvious phenomenon of charge transfer is present between Mg atoms in the first layer of the MgH2 (110) crystal face and O atoms in the nitro group of RDX. Also, the charge change in O and Mg atoms in the V configuration is greater than that in the P configuration, indicating that the V configuration has stronger interaction between RDX and the MgH2 (110) crystal face, and thus RDX in the V configuration is more prone to decomposition and the V configuration represents a better adsorption mode.

Datum: 24.09.2017

A test of the significance of intermolecular vibrational coupling in isotopic fractionation

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Michael F. Herman, Robert P. Currier, Travis B. Peery, Samuel M. Clegg

Intermolecular coupling of dipole moments is studied for a model system consisting of two diatomic molecules (AB monomers) arranged co-linearly and which can form non-covalently bound dimers.The dipolar coupling is a function of the bond length in each molecule as well as of the distance between the centers-of-mass of the two molecules. The calculations show that intermolecular coupling of the vibrations results in an isotope-dependent modification of the AB-AB intermolecular potential. This in turn alters the energies of the low-lying bound states of the dimers, producing isotope-dependent changes in the AB-AB dimer partition function. Explicit inclusion of intermolecular vibrational coupling then changes the predicted gas-dimer isotopic fractionation. In addition, a mass dependence in the intermolecular potential can also result in changes in the number of bound dimer states in an equilibrium mixture. This in turn leads to a significant dimer population shift in the model monomer-dimer equilibrium system considered here. The results suggest that intermolecular coupling terms should be considered when probing the origins of isotopic fractionation.

Datum: 24.09.2017

Preparation and characterization of bio resin natural tannin/poly (vinylidene fluoride): A high dielectric performance nano-composite for electrical storage

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): S. Abdalla, A. Pizzi, Maryam A. Al-Ghamdi, Reem AlWafi

We have prepared films of polymer nano-composite (PNC) of poly [vinylidene-fluoride] (PVDF) and bio resin natural tannin (BRNT) nanoparticles. The α and γ electro-active phases were detected, and the addition of BRNT drastically increases the formation of the α-phase. Addition of BRNT produces up to 98% of electro-active phases. Robust electrostatic interactions arise between charges at the BRNT-surfaces, and differences in electron affinity between CH2 and CF2 groups created dielectric dipoles. The addition of BRNT has not only enhanced the formation of the electrically active phases but also makes each dipole in the phase has its specific characteristics for example its own relaxation time. The AC-electrical permittivity showed that the dielectric constant of 10%wt-BRNT nanoparticles in PVDF has a value 44 ε0, which is four times more than the dielectric constant of the as-prepared PVDF films. These data show the importance of these polymers as easy, flexible, and durable energy storage materials.

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Datum: 24.09.2017

Molecular dynamics of supercooled ionic liquids studied by light scattering and dielectric spectroscopy

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Florian Pabst, Jan Gabriel, Peter Weigl, Thomas Blochowicz

We investigate molecular dynamics of two supercooled room temperature ionic liquids (RTILs) above of their glass transition temperature by means of dynamic light scattering and broadband dielectric spectroscopy from nanoseconds up to $≈ 10 5 s$. We show that a direct comparison of the raw data of these two techniques allows us to identify the reorientation of ions in the dielectric data, giving experimental evidence to a very recently proposed model of Gainaru et al. [1], stating that the conductivity process in ionic liquids takes place through a reorientational step of ions escaping their cage formed by surrounding counterions. Within this approach we can also understand the apparent decoupling of time constants from dielectric spectroscopy and light scattering, often found in ionic liquids, in a very natural way. Furthermore, as a consequence of knowing the reorientational part of the dielectric spectrum, we are able to show that two more processes contribute to these spectra, which are due to electrode polarization effects. The relative position of all three contributions vary among the systems and may overshadow each other, thus complicating the data analysis and favor misinterpretations.

Datum: 24.09.2017

IFC (Editorial Board)

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Datum: 24.09.2017

Modeling the THF Clathrate Hydrate Dynamics by combining Molecular Dynamics and Quasi-Elastic Neutron Scattering

Publication date: Available online 22 September 2017
Source:Chemical Physics

Author(s): Eric Pefoute, Ludovic Martin-Gondre, Jacques Ollivier, Jean-Christophe Soetens, Margarita Russina, Arnaud Desmedt

The dynamics of the THF molecule encapsulated in the type II clathrate hydrate matches the MD-QENS observation time (typically 0.1-10 ps) between 100K and 270K. Spatial and time characteristics of the THF molecule’s dynamics obtained by means of MD simulations are in agreement with those experimentally determined by means of quasielastic neutron scattering. A detailed model of the THF dynamics is then proposed through the calculations of MD-derived properties. Reorientational relaxation has been observed on a timescale of 0.7 ± 0.1 ps at 270K with activation energy of 3.0±0.3kJ/mol in addition to a highly damped rotational excitation occurring in the plane of the THF molecule with a period of ca. 2 ps. Moreover, the anisotropic cage energy landscape of the THF clathrate hydrate is revealed through a comprehensive investigation of THF orientational distribution functions, revealing the occurrence of preferred orientation of the THF molecule within the cage.

Datum: 24.09.2017

A comprehensive comparison between thermodynamic perturbation theory and first-order mean spherical approximation: Based on discrete potentials with hard core

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Shiqi Zhou, Run Zhou

Using the TL (Tang and Lu, 1993) method, Ornstein-Zernike integral equation is solved perturbatively under the mean spherical approximation (MSA) for fluid with potential consisting of a hard sphere plus square-well plus square-shoulder (HS + SW + SS) to obtain first-order analytic expressions of radial distribution function (RDF), second-order direct correlation function, and semi-analytic expressions for common thermodynamic properties. A comprehensive comparison between the first-order MSA and high temperature series expansion (HTSE) to third-, fifth- and seventh-order is performed over a wide parameter range for both a HS + SW and the HS + SW + SS model fluids by using corresponding “exact” Monte Carlo results as a reference; although the HTSE is carried out up to seventh-order, and not to the first order as the first-order MSA the comparison is considered fair from a calculation complexity perspective. It is found that the performance of the first-order MSA is dramatically model-dependent: as target potentials go from the HS + SW to the HS + SW + SS, (i) there is a dramatic dropping of performance of the first-order MSA expressions in calculating the thermodynamic properties, especially both the excess internal energy and constant volume excess heat capacity of the HS + SW + SS model cannot be predicted even qualitatively correctly. (ii) One tendency is noticed that the first-order MSA gets more reliable with increasing temperatures in dealing with the pressure, excess Helmholtz free energy, excess enthalpy and excess chemical potential. (iii) Concerning the RDF, the first-order MSA is not as disappointing as it displays in the cases of thermodynamics. (iv) In the case of the HS + SW model, the first-order MSA solution is shown to be quantitatively correct in calculating the pressure and excess chemical potential even if the reduced temperatures are as low as 0.8. On the other hand, the seventh-order HTSE is less model-dependent; in most cases of the HS + SW and the HS + SW + SS models, the seventh-order HTSE improves the fifth- and third-order HTSE in both thermodynamic properties and RDF, and the improvements are very demonstrable in both the excess internal energy and constant volume excess heat capacity; for very limited cases, the seventh-order HTSE improves the fifth-order HTSE only within lower density domain and even shows a bit of inadaptation over higher density domain.

Datum: 24.09.2017

Adsorption of ethylene carbonate on lithium cobalt oxide thin films: A synchrotron-based spectroscopic study of the surface chemistry

Publication date: Available online 11 September 2017
Source:Chemical Physics

Author(s): Mathias Fingerle, Thomas Späth, Natalia Schulz, René Hausbrand

The surface chemistry of the cathode material lithium cobalt oxide (LiCoO2) in contact with the Li-ion battery solvent ethylene carbonate (EC) was studied by means of synchrotron based soft X-ray photoelectron spectroscopy (SXPS). By stepwise in-situ adsorption of EC onto a rf-magnetron sputtered LiCoO2 thin film and consecutive recording of SXPS spectra, the chemical and electronic properties of the interface were determined allowing to deduce the behavior of lithium ions. Physisorption as well as decomposition can be detected for the EC molecules forming a complex reaction layer, as common for a solid electrolyte interface (SEI) in lithium ion secondary batteries. Upon interface formation, lithium ions deintercalate from the electrode and are dissolved in the adsorbate phase.

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Datum: 24.09.2017

Contents

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Datum: 24.09.2017

IFC (Editorial Board)

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Datum: 24.09.2017

Benzodichalcogenophene-diketopyrrolopyrrole small molecules as donors for efficient solution processable solar cells

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Ling Fan, Guohui Chen, Lihui Jiang, Jun Yuan, Yingping Zou

Three small molecules named BDTDPP, TBFDPP and BDFDPP are designed and synthesized with alkoxy-substituted benzodichalcogenophene derivatives as donor unit while diketopyrrolopyrrole unit as acceptor unit, the investigation results show that all three small molecular materials possess favorable solubility, excellent thermal stability, broad absorption spectra and suitable electrochemical energy level. The bulk heterojunction devices based on these three small molecular materials show the power conversion efficiencies up to 3.19%, 2.82% and 2.81%, respectively. When adding 0.3% (v/v) 1,8-diiodooctane as additives, the power conversion efficiencies were further improved to 3.95%, 3.72% and 3.41%, respectively. The investigations show that all three benzodichalcogenophene-diketopyrrolopyrrole derivatives have great potential in the design of high performance optoelectronic materials.

Datum: 24.09.2017

Electronic structures and population dynamics of excited states of xanthione and its derivatives

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Roman G. Fedunov, Marina V. Rogozina, Svetlana S. Khokhlova, Anatoly I. Ivanov, Sergei A. Tikhomirov, Stanislav L. Bondarev, Tamara F. Raichenok, Oleg V. Buganov, Vyacheslav K. Olkhovik, Dmitrii A. Vasilevskii

A new compound, 1,3-dimethoxy xanthione (DXT), has been synthesized and its absorption (stationary and transient) and luminescence spectra have been measured in n-hexane and compared with xanthione (XT) spectra. The pronounced broadening of xanthione vibronic absorption band related to the electronic transition to the second singlet excited state has been observed. Distinctions between the spectra of xanthione and its methoxy derivatives are discussed. Quantum chemical calculations of these compounds in the ground and excited electronic states have been accomplished to clarify the nature of electronic spectra changes due to modification of xanthione by methoxy groups. Appearance of a new absorption band of DXT caused by symmetry changes has been discussed. Calculations of the second excited state structure of xanthione and its methoxy derivatives confirm noticeable charge transfer (about 0.1 of the charge of an electron) from the methoxy group to thiocarbonyl group. Fitting of the transient spectra of XT and DXT has been fulfilled and the time constants of internal conversion $S 2 → S 1$ and intersystem crossing $S 1 → T 1$ have been determined. A considerable difference between the time constants of internal conversion $S 2 → S 1$ in XT and DXT is uncovered.

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Datum: 24.09.2017

Vibrational spectroscopy modeling of a drug in molecular solvents and enzymes

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Christian J. Devereux, Kristen D. Fulfer, Xiaoliu Zhang, Daniel G. Kuroda

Modeling of drugs in enzymes is of immensurable value to many areas of science. We present a theoretical study on the vibrational spectroscopy of Rilpivirine, a HIV reverse transcriptase inhibitor, in conventional solvents and in clinically relevant enzymes. The study is based on vibrational spectroscopy modeling of the drug using molecular dynamics simulations, DFT frequency maps, and theory. The modeling of the infrared lineshape shows good agreement with experimental data for the drug in molecular solvents where the local environment motions define the vibrational band lineshape. On the other hand, the theoretical description of the drug in the different enzymes does not match previous experimental findings indicating that the utilized methodology might not apply to heterogeneous environments. Our findings show that the lack of reproducibility might be associated with the development of the frequency map which does not contain all of the possible interactions observed in such systems.

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Datum: 24.09.2017

Theoretical prediction of noble gas inserted halocarbenes: FNgCX (Ng=Kr, and Xe; X=F, Cl, Br, and I)

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Pragya Chopra, Ayan Ghosh, Banasri Roy, Tapan K. Ghanty

A new series of neutral noble gas inserted compounds involving halocarbenes, mainly, FNgCX (Ng=Kr, and Xe; X=F, Cl, Br, and I) has been predicted through various ab initio quantum chemical techniques such as MP2, DFT, CCSD(T) and MRCI. The structure, stabilities, charge distribution, harmonic vibrational frequencies and topological properties of these compounds have been investigated. It is found that the predicted species are energetically stable with respect to all the plausible 2-body and 3-body dissociation pathways, with the exception of the 2-body channel that leads to the global minimum products (FCX+Ng). Despite this, existence of finite barrier heights indicates that these compounds are kinetically stable with respect to global minimum products. The computational results indicate that it might be possible to prepare and characterize the most stable singlet state of FNgCX molecules under cryogenic conditions through suitable experimental technique(s).

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Datum: 24.09.2017

Cluster formation and percolation in ethanol-water mixtures

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Author(s): Orsolya Gereben, László Pusztai

Results of systematic molecular dynamics studies of ethanol-water mixtures, over the entire concentration range, were reported previously that agree with experimental X-ray diffraction data. These simulated systems are analyzed in this work to examine cluster formation and percolation, using four different hydrogen bond definitions. Percolation analyses revealed that each mixture (even the one containing 80mol% ethanol) is above the 3D percolation threshold, with fractal dimensions, df , between 2.6 and 2.9, depending on concentration. Monotype water cluster formation was also studied in the mixtures: 3D water percolation can be found in systems with less than 40mol% ethanol, with fractal dimensions between 2.53 and 2.84. These observations can be put in parallel with experimental data on some thermodynamic quantities, such as the excess partial molar enthalpy and entropy.

Datum: 24.09.2017

Irreversible thermodynamic analysis and application for molecular heat engines

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Umberto Lucia, Emin Açıkkalp

Is there a link between the macroscopic approach to irreversibility and microscopic behaviour of the systems? Consumption of free energy keeps the system away from a stable equilibrium. Entropy generation results from the redistribution of energy, momentum, mass and charge. This concept represents the essence of the thermodynamic approach to irreversibility. Irreversibility is the result of the interaction between systems and their environment. The aim of this paper is to determine lost works in a molecular engine and compare results with macro (classical) heat engines. Firstly, irreversible thermodynamics are reviewed for macro and molecular cycles. Secondly, irreversible thermodynamics approaches are applied for a quantum heat engine with -1/2 spin system. Finally, lost works are determined for considered system and results show that macro and molecular heat engines obey same limitations. Moreover, a quantum thermodynamic approach is suggested in order to explain the results previously obtained from an atomic viewpoint.

Datum: 24.09.2017

Adsorption of O, O2 and CO on iridium clusters and the investigations of their stability

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Muna Tayyem, Bothina Hamad, Beate Paulus

Density functional theory calculations were performed to study the stability of Irn clusters as well as the adsorption of O, O2 and CO adsorbates on selected structures. The clusters form three dimensional structures for n&gt;4. Larger clusters of n&gt;13 exhibit simple cubic structures up to n around 32, beyond which fcc structures become more favorable. The binding energy is found to increase as a function of cluster size to approach bulk cohesive energy asymptotically. The total magnetic moment is found to decrease as a function of the cluster size approaching the bulk nonmagnetic ground state. The top adsorption site is the most site of O, O2 and CO on small clusters, unlike Ir64 that exhibits hollow, bridge and top sites, respectively. The vibrational frequencies of CO (O2) on Ir2 and Ir4 are found to be less than those of free molecules of 2102.82 (1562.08)cm−1.

Datum: 24.09.2017

Wavelength dependence of high-harmonic yield in stretched molecules

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Shengjun Yue, Hongchuan Du, Hongmei Wu, Jinbin Li, Bitao Hu

We study the wavelength dependence of harmonic yield in stretched molecules. It is found that when the laser field is perpendicular to the molecular axis, the harmonic yield has a slow scaling $λ - 4.27$ as the increase of the laser wavelength for the stretched molecule $H 2 +$ with the internuclear distance of 7a.u. compared with $λ - 5.11$ for $H 2 +$ at the equilibrium position. Further analysis shows that the narrower width of the initial wave-function in the momentum space is in charge of the slow wavelength scaling of the stretched molecule since it can make the wave-function spreading less during propagation. Moreover, a higher enhancement and a better wavelength scaling of harmonic yield both can be achieved at the optimal internuclear distance of 7a.u.

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Datum: 24.09.2017

AIMS simulation study of ultrafast electronically nonadiabatic chemistry of methyl azide and UV–VIS spectroscopic study of azido-based energetic plasticizer bis(1,3-diazido prop-2-yl)malonate

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Jayanta Ghosh, Shaibal Banerjee, Atanu Bhattacharya

To gain insight into the ultrafast electronically nonadiabatic chemistry of azido-based energetic plasticizer, we have explored the nonadiabatic chemical dynamics of an azido-based model analog molecule, methyl azide (MAz), using ab initio multiple spawning (AIMS) simulation and electronic structure theory calculations. Molecular nitrogen (N2) is predicted to be the initial product of MAz following its electronic excitation to the S1 electronically excited state. AIMS-based simulation reveals that electronically excited azido-based molecules undergo extremely fast (approximately in 40 femtoseconds) relaxation to the ground state via the (S1/S0)CI conical intersection. Furthermore, this relaxation process involves the NN bond elongation along with the bending of N3 moiety. This is the first report on the electronically non-adiabatic chemical dynamics (in ultrafast time domain) of methyl azide. Finally, using ultraviolet–visible (UV–VIS) spectroscopy, we comment on the electronically nonadiabatic chemistry of azido-based energetic plasticizer, bis(1,3-diazido prop-2-yl)malonate.

Datum: 24.09.2017

Shell effect on the electron and hole reorganization energy of core-shell II–VI nanoclusters

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Xianhui Cui, Xinqin Wang, Fang Yang, Yingqi Cui, Mingli Yang

Density functional theory calculations were performed to study the effect of shell encapsulation on the geometrical and electronic properties of pure and hybrid core-shell CdSe nanoclusters. The CdSe cores are distorted by the shells, and the shells exhibit distinct surface activity from the cores, which leads to remarkable changes in their electron transition behaviors. Although the electron and hole reorganization energies, which are related to the formation and recombination of electron-hole pairs, vary in a complicated way, their itemized contributions, potentials of electron extraction, ionization and affinity, and hole extraction (HEP), are dependent on the cluster size, shell composition and/or solvent. Our calculations suggest that the behaviors of charge carriers, free electrons and holes, in the semiconductor core-shell nanoclusters can be modulated by selecting appropriate cluster size and controlling the chemical composition of the shells.

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Datum: 24.09.2017

About mobility thickness dependence in molecularly doped polymers

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): A.P. Tyutnev, D.S. Weiss, V.S. Saenko, E.D. Pozhidaev

We have investigated the dependence of hole mobility on thickness in free-standing films of bisphenol-A-polycarbonate (PC) doped with 30wt% p-diethylaminobenzaldehyde diphenylhydrazone (DEH). Carrier generation in a time-of-flight (TOF) experiment was achieved through direct ionization of dopant molecules by electron impact using an electron gun supplying pulses of monoenergetic electrons in the range of 2–50keV. The position of dopant ionization depends upon the electron energy and three TOF variants have been recently developed and used in this study. We have found that the hole mobility generally decreased with increasing film thickness with concomitant acceleration of the post-flight current decay indicating that the transport process approaches the steady-state regime, this process happening slightly faster than our model predicts. Numerical calculations have been compared with experimental data. The results are discussed in detail. The way to reconcile ostensibly contradictory interpretations of our results and those commonly reported in literature relying on photo injection technique has been proposed.

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Datum: 24.09.2017

Analysis of the non-Markovianity for electron transfer reactions in an oligothiophene-fullerene heterojunction

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): E. Mangaud, C. Meier, M. Desouter-Lecomte

The non-Markovianity of the electron transfer in an oligothiophene-fullerene heterojunction described by a spin-boson model is analyzed using the time dependent decoherence canonical rates and the volume of accessible states in the Bloch sphere. The dynamical map of the reduced electronic system is computed by the hierarchical equations of motion methodology (HEOM) providing an exact dynamics. Transitory witness of non-Markovianity is linked to the bath dynamics analyzed from the HEOM auxiliary matrices. The signature of the collective bath mode detected from HEOM in each electronic state is compared with predictions of the effective mode extracted from the spectral density. We show that including this main reaction coordinate in a one-dimensional vibronic system coupled to a residual bath satisfactorily describes the electron transfer by a simple Markovian Redfield equation. Non-Markovianity is computed for three inter fragment distances and compared with a priori criterion based on the system and bath characteristic timescales.

Datum: 24.09.2017

IFC (Editorial Board)

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Datum: 24.09.2017

Multimodal hyperspectral optical microscopy

Publication date: Available online 2 September 2017
Source:Chemical Physics

Author(s): Irina V. Novikova, Chuck R. Smallwood, Yu Gong, Dehong Hu, Leif Hendricks, James E. Evans, Ashish Bhattarai, Wayne P. Hess, Patrick Z. El-Khoury

We describe a unique approach to hyperspectral optical microscopy, herein achieved by coupling a hyperspectral imager to various optical microscopes. Hyperspectral fluorescence micrographs of isolated fluorescent beads are first employed to ensure spectral calibration of our detector and to gauge the attainable spatial resolution of our measurements. Different science applications of our instrument are then described. Spatially over-sampled absorption spectroscopy of a single lipid (18:1 Liss Rhod PE) layer reveals that optical densities on the order of 10−3 can be resolved by spatially averaging the recorded optical signatures. This is followed by three applications in the general areas of plasmonics and bioimaging. Notably, we deploy hyperspectral absorption microscopy to identify and image pigments within a simple biological system, namely, a single live Tisochrysis lutea cell. Overall, this work paves the way for multimodal spectral imaging measurements spanning the realms of several scientific disciplines.

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Datum: 24.09.2017

Benzophenone as a photoprobe of polymer films

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Peter P. Levin, Alexei F. Efremkin, Igor V. Khudyakov

The review article is devoted to kinetics of fast reactions following photoexcitation of benzophenone in polymer films. We observed three processes by ns laser flash photolysis in elastomers: (i) decay of a triple state of benzophenone with hydrogen abstraction from polymer matrix, (ii) formation and decay of geminate radical pairs, (iii) cross-termination of the formed radicals in the polymer bulk. Application of external magnetic field (MF) of B =0.2T essentially affects recombination of geminate (G-) and a bimolecular recombination of free radicals, which escaped polymer cage (F-pairs). Theoretical calculation of MF effects on G- and F-pairs is in agreement with corresponding experimental data. Elongation of elastomer leads to an unexpected observation: recombination in the bulk becomes slower. An explanation of this phenomenon based on elastomer free volume Vf approach was suggested.

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Datum: 24.09.2017

Contents

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Datum: 24.09.2017

Some possible channels for the N2 formation and their probable effects on the interstellar elemental nitrogen partitioning: A computational study

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Priya Bhasi, Zanele P. Nhlabatsi, Sanyasi Sitha

Nitrogen content of the interstellar regions is undergoing a re-evaluation based on some recent comet data and some excellent researches in this area. Finding of secondary channels for the formation of N2 will definitely have significant effect in accounting the elemental nitrogen partitioning and also the active nitrogen chemistry of the interstellar medium. In this work, computational calculations of potential energy surface for the reaction between NS and NSi has been carried out. We were able to locate many dissociation channels leading to the formation of N2 from some of these isomers, both in singlet as well as the triplet potential energy surfaces. Based on the analysis of the dissociation paths, it has been argued that such dissociation reactions leading to the formation of N2 will be possible not only in hot-cores, but also in the cold interstellar clouds of the interstellar medium.

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Datum: 24.09.2017

Can DFT and ab initio methods adequately describe binding energies in strongly interacting C6X6⋯C2Xn π–π complexes?

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Berthelot Saïd Duvalier Ramlina Vamhindi, Amir Karton

We calculate the CCSD(T)/CBS complexation energies of C6X6⋯C2X n complexes (X=F, Cl; n =2, 4) by means of the W1-F12 and CCSD(T)/MP2(CBS) procedures. These complexes involve π–π stacking, charge-transfer, and van der Waals interactions and their complexation energies range between 11.1 (C6F6⋯C2F2) and 34.0 (C6Cl6⋯C2Cl4)kJmol 1. We use our best CCSD(T)/CBS data to assess the performance of DFT, double-hybrid DFT (DHDFT), and standard/composite ab initio methods. The G4 and G4(MP2) composite methods show relatively poor performance with root-mean-square deviations (RMSDs) of 8.7 and 6.3kJmol 1, respectively. With the main exception of the Minnesota functionals, DFT functionals without a dispersion correction do not predict binding in these complexes. Most of the conventional DFT procedures attain RMSDs above the ‘chemical accuracy’ threshold. The best performing functionals with RMSDs ≤2.0kJmol 1 are: B3LYP-D3, PW6B95-D3, LC-ωPBE-D3, PWPB95-D3, B2GP-PLYP-D3, and B2-PLYP-D3.

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Datum: 24.09.2017

Two types of coherence resonance in an intracellular calcium oscillation system

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Juan Ma, Qingyu Gao

Two types of noise induced oscillations (NIOs) near Hopf bifurcation and coherence resonance (CR) have been studied analytically in a calcium system. One is NIOs with small amplitude and internal signal stochastic resonance (CR type I) occurs, and the other is noise induced spike and the regularity of which reaches a maximum at an optimal noise level (CR type II). For the first type, stochastic normal form theory is employed to analyze the signal to noise ratio of the NIOs depending on the noise intensity. For the second type, based on the independent assumption, activation time and excursion time have been split, and the sum of which reach a minimum with the variation of noise intensity. The theoretical evidence is also explained in detail. Numerical simulations show good agreements with the theoretical results. It may indicate some kind of transmit mechanism involved in stochastic calcium dynamics.

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Datum: 24.09.2017

Magnetic-field dependence of the impurity states in a dome-shaped quantum dot

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): E.C. Niculescu, C. Stan, M. Cristea, C. Truscă

Using the finite element method, the effect of magnetic fields on the donor states and transition energies in a InAs/GaAs quantum dot coupled to its wetting layers is investigated. Results are obtained for different impurity locations. We found that the diamagnetic shift of the ground state energy increases monotonously with the applied field and can be described by a simple function which interpolates between the low and high magnetic-field behavior. Frequencies associated to the transitions between the S-like ground state and P (P +) excited states range in terahertz region and show a magnetic field-induced red (blue) shift, irrespectively of the impurity position.

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Datum: 24.09.2017

Real-time observation of interfragment vibration and charge transfer within the TCNQF4 dimer

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Sena Hashimoto, Atsushi Yabushita, Izumi Iwakura

The organic electron acceptors, 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF4), are widely used to synthesize multivalent charge-transfer complexes. Their corresponding radical anion complexes have specific electronic, optical, and magnetic characters that have attracted attention in the field of materials development. In the present work, we have performed time-resolved absorption spectroscopy of the (Na+)2(TCNQF4 )2 radical anion complex to elucidate the reaction dynamics ([TCNQF4 ]2 TCNQF4 +TCNQF4 2−). A visible sub-10fs laser pulse was used to observe the ultrafast dynamics of the charge transfer and real-time change of the molecular structure during the reaction. Unlike our previous work on the (Na+)2(TCNQ )2 radical anion complex, the interfragment vibrational mode was clearly observed for (Na+)2(TCNQF4 )2. The difference in the intermolecular interaction is considered to reflect the difference in the π-π interaction and/or the difference in the flexibility of the molecular plane predicted by theoretical calculations.

Datum: 24.09.2017

Electronic structure of Fe, α-Fe2O3 and Fe(NO3)3×9 H2O determined using RXES

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Michał Nowakowski, Joanna Czapla-Masztafiak, Jakub Szlachetko, Wojciech M. Kwiatek

Resonant X-ray emission spectroscopy (RXES) technique was applied to probe electronic states of three Fe compounds: Fe, α-Fe2O3 (hematite) and Fe(NO3)3 ×9 H2O (ferric nitrate) around Fe K-absorption edge with simultaneous detection of Kβ and valence-to-core transitions. We show that deep insights on the valence and conduction band position, such as main orbital contribution to band-gap formation and ligand orbital contributions, can be retrieved from RXES data. Moreover applicability of Kβ and valence-to-core RXES measurements to extract band gap energies is demonstrated. Obtained results were supplemented with ab initio calculations allowing precise determination of orbital contributions to the measured spectral features. Good agreement with experimental results has shown that proposed approach is promising tool in further applications.

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Datum: 24.09.2017

Investigation on electronic properties of functionalized arsenene nanoribbon and nanotubes: A first-principles study

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): V. Nagarajan, R. Chandiramouli

The electronic properties of arsenene nanotubes and nanoribbons with hydrogenation along the zigzag and armchair edges are studied using density functional theory (DFT) technique. The structural stability of hydrogenated zigzag and armchair arsenene nanostructures are confirmed with formation energy. The electronic properties of arsenene nano-conformers are described in terms of energy band structure and projected density of states spectrum. Furthermore, owing to the influence of hydrogen passivation, buckled orientation and width of arsenene nanostructures, the band gap widens in the range of 0.38–1.13eV. The findings of the present work confirm that the electronic properties of arsenene nanomaterial, can be fine-tuned with the influence of passivation with hydrogen, zigzag or armchair border shapes and effect of the width of nanoribbons or nanotubes, which can be utilized as spintronic device and chemical sensor.

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Datum: 24.09.2017

Quantum chemical study of small AlnBm clusters: Structure and physical properties

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Boris I. Loukhovitski, Alexander S. Sharipov, Alexander M. Starik

The structure and physical properties, including rotational constants, characteristic vibrational temperatures, collision diameter, dipole moment, static polarizability, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and formation enthalpy of the different isomeric forms of $Al n B m$ clusters with $n + m ⩽ 7$ are studied using density functional theory. The search of the structure of isomers has been carried employing multistep hierarchical algorithm. Temperature dependencies of thermodynamic functions, such as enthalpy, entropy, and specific heat capacity, have been determined both for the individual isomers and for the ensembles with equilibrium and frozen compositions for the each class of clusters taking into account the anharmonicity of cluster vibrations and the contribution of their excited electronic states. The prospects of the application of small $Al n B m$ clusters as the components of energetic materials are also considered.

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Datum: 24.09.2017

Characteristics of methylammonium ion (CH3NH3+) in aqueous electrolyte solution: An ONIOM-XS MD simulation study

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Prangthong Chaiyasit, Anan Tongraar, Teerakiat Kerdcharoen

An ONIOM-XS MD simulation has been performed to characterize the CH3NH3 +-water hydrogen bonds (HBs) in aqueous solution. The sphere which includes the CH3NH3 + ion and its surrounding waters was treated by the HF/DZP method, while the rest was described by classical pair potentials. The ONIOM-XS MD results clearly reveal a flexible CH3NH3 + solvation, showing various numbers of water molecules, ranging from 3 to 8 and from 12 to 19, cooperatively involved in the primary region of the NH3 + and CH3 species, respectively. The NH3 + group participates in about 3.6 HBs with its nearest-neighbor waters, and the HBs between the NH3 + hydrogens and their nearest-neighbor waters are relatively weaker than the HBs of bulk water. It is evident that the “hydrophobic effect” of the CH3 species results in slightly more attractive water-water HB interactions in this region. Such phenomenon corresponds to a clear “structure-breaking” ability of CH3NH3 + in aqueous solution.

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Datum: 24.09.2017

Reversible hydrogen adsorption on Co/N4 cluster embedded in graphene: The role of charge manipulation

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Akbar Omidvar

Electrical charging of Co/N4 cluster embedded in graphene (Co/N4/G) is proposed as an approach for electrocatalytically switchable hydrogen adsorption. Using density functional theory, we found that the H2 molecule is weakly adsorbed on the uncharged Co/N4/G cluster. Our results show that the adsorption energy of hydrogen molecule on Co/N4/G cluster is significantly increased by introducing extra positive charges into the cluster. Once the charges are removed, H2 molecule spontaneously desorb from the Co/N4/G absorbent. Therefore, this approach promises both facile reversibility and tunable kinetics without the need of specific catalysts. Our study indicates that the Co/N4/G nanomaterial is excellent absorbent for controllable and reversible adsorption and release of H2.

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Datum: 24.09.2017

Simultaneous effects of pressure and temperature on the optical transition energies in a Ga0.7In0.3N/GaN quantum ring

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): K. Jaya Bala, A. John Peter, Chang Woo Lee

Simultaneous effects of pressure and temperature on electronic and optical properties are studied in a Ga0.7In0.3N/GaN quantum ring using variational formulism. The changes in exciton binding energy due to the applications of hydrostatic pressure and temperature are obtained taking into account the geometrical confinement. The transition energies of interband and intersubband as a function of hydrostatic pressure, at a constant temperature, are obtained. The oscillator strength due to interband and intersubband optical transitions with the combined effects of hydrostatic pressure and temperature is found. The pressure and temperature induced absorption coefficients as a function of photon energy are investigated in a Ga0.7In0.3N/GaN quantum ring. The results show that the application of pressure leads to blue shift of the resonant peaks of the optical transition whereas the effect of temperature suffers red shift of the resonant peaks.

Datum: 24.09.2017

Natural optical activity of f-f transitions in ErAl3(BO3)4 single crystal

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): A.V. Malakhovskii, V.V. Sokolov, I.A. Gudim

Absorption and natural circular dichroism (NCD) spectra of ErAl3(BO3)4 single crystal were measured at 90K in the range of 10,000–28,200cm−1. The spectra were decomposed on the Lorentz shape components and the natural optical activities (NOA) of f-f transitions between Stark components of the ground and excited multiplets were found. The NCD spectra permitted us to find out existence of two non equivalent positions of Er3+ ion in one of its excited states, which are due to the local decrease of the crystal symmetry in this state. Very large NOA of a vibronic line was revealed. This phenomenon was accounted for basing on the new quantum mechanical formula for the NOA of electron transitions. The principle difference of the NOA properties of electric dipole allowed and parity forbidden transitions is discussed.

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Datum: 24.09.2017

Temperature dependence of the spin relaxation time of Fe3O4 and hemozoin superparamagnetic nanocrystals

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): I. Khmelinskii, V. Makarov

We report experimental temperature and concentration dependences of the natural spin relaxation time of superparamagnetic Fe3O4 and hemozoin nanocrystals. We recorded the 1H NMR spectrum of 0.5% benzene dissolved in CS2 in function of superparamagnetic particle concentration and temperature, interpreting the 7.261±0.002ppm benzene line broadening. Our model for the line broadening includes natural, hyperfine magnetic dipole-dipole, and contact hyperfine contributions. The latter arises due to exchange interaction between benzene molecules and suspended nanoparticles. Estimated frequency of fluctuation in the 1 cm3 sample volume is in the 107 Hz scale. Estimated natural electron spin-lattice relaxation frequencies of the superparamagnetic nanocrystals using frequency of fluctuations, and developed theoretical model applied to analysis of experimental data are in good agreement between each other. Thus the presently developed approach may be used to study fluctuations and natural spin-lattice relaxation frequencies in different media.

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Datum: 24.09.2017

Transport coefficients and validity of the Stokes-Einstein relation in metallic melts: From excess entropy scaling laws

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): Ruchi Shrivastava, Raj Kumar Mishra

Using the pair correlation function obtained via square well (SW) model [Mishra et al., 2015 Chem. Phys. 457 13], we calculate the pair excess entropy of liquid metals and determined the diffusion coefficients via Dzugutov’s excess entropy-diffusivity scaling relation. Further, the applicability of the Stokes-Einstein relation for SW potential is validated by comparing the computed shear viscosity coefficients (ηV ) of liquid metals with the available experimental data. Reduced ηV of considered systems has been derived and scaled with the excess entropy. We compute isothermal compressibility, surface tension and surface entropy of the investigated liquids by using diffusion coefficient data obtained from excess entropy scaling law. It is found that the computed values are in good agreement with the corresponding experimental data. Thus, we demonstrate that the Dzugutov scheme can be applied successfully to SW liquid metals to correlate their microscopic structural functions with their surface and thermodynamic properties.

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Datum: 24.09.2017

Molecular dynamics simulation study of hydration of uranyl nitrate in supercritical water: Dissecting the effect of uranyl ion concentration from solvent density

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Manish Chopra, Niharendu Choudhury

All atom molecular dynamics simulations of uranyl ions in supercritical water are used to dissect the effects of concentration of uranyl ions and density of water on various structural and dynamic properties of the solutions. The analyses of radial distribution functions as a function of concentration of the uranyl ion and water density reveal that the effect of the former on the local structure is negligible as compared to the same of the later. The number of hydration water of the uranyl ion has been observed to increase with increasing density of the water, but it decreases with the increasing concentration of the uranyl ions. The orientational distributions are observed to be independent of variation in concentration of the uranyl ion, same as the case was with water density. The translational and rotational dynamics of the water molecules have been investigated from the respective mean squared displacements and time correlation functions. Although increase of both the concentration of the uranyl ions and the density of water reduces translational diffusivity of water as well as uranyl ions, the effect of changing water density is more than that of uranyl concentrations. However, orientational relaxation of various molecular vectors of the water molecule is practically unchanged with any variation in concentration of the uranyl ions and it changes only slightly with the change in water density. Unlike at ambient condition, orientational dynamics at supercritical conditions remains virtually unchanged with the change in uranyl ion concentration.

Datum: 24.09.2017

An exactly solvable model of polymerization

Publication date: 17 August 2017
Source:Chemical Physics, Volume 493

Author(s): A.A. Lushnikov

This paper considers the evolution of a polydisperse polymerizing system comprising $g 1 , g 2 …$ – mers carrying $ϕ 1 , ϕ 2 …$ functional groups reacting with one another and binding the g-mers together. In addition, the g-mers are assumed to be added at random by one at a time with a known rate depending on their mass g and functionality $ϕ$. Assuming that the rate of binding of two g-mers is proportional to the product of the numbers of nonreacted functional groups the kinetic equation for the distribution of clusters (g-mers) over their mass and functionalities is formulated and then solved by applying the generating function method. In contrast to existing approaches this kinetic equation operates with the efficiencies proportional to the product of the numbers of active functional groups in the clusters rather than to the product of their masses. The evolution process is shown to reveal a phase transition: the emergence of a giant linked cluster (the gel) whose mass is comparable to the total mass of the whole polymerizing system. The time dependence of the moments of the distribution of linked components over their masses and functionalities is investigated. The polymerization process terminates by forming a residual spectrum of sol particles in addition to the gel.

Datum: 24.09.2017

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