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Journal of Structural Chemistry

2013 year, number 2

1.
Statistical mechanics and Fluid structure

G.A. Martynov
A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Moscow
Keywords: statistical mechanics, axiomatic approach, correlation sphere, fluid structure

Abstract >>
In the axiomatic approach to the derivation of statistical mechanics the theory is based upon the equations of motions of classical mechanics (Hamilton equations). Since these equations are unstable with respect to initial conditions, in the time τ ≈ 10–12 s they generate chaos in the system of atoms and molecules. This chaos can be described by only probability theory laws. The laws of this theory are introduced into statistical mechanics as the second postulate. However, for both postulates (i.e., Hamilton equations and probability theory laws) to be compatible with each other, about one and a half ten of additional requirements defining in detail the matter model underlying the theory must be imposed on the system. This report analyzes only the restrictions imposed by probability theory. The main of them are: a transition to the thermodynamic limit, the condition of correlation attenuation, and a short-range character of the interaction potential. The matter model formulated based on these restrictions is a continuous medium in which a correlation sphere with a small radius R≈ 107 cm (physical point) is submerged. It is submerged in an infinite thermostat, the particles of which behave as the ideal gas relative to the particles forming the correlation sphere. Here all macroscopic parameters of matter in this physical point are determined by the state of the correlation sphere. Thus formulated model determines the macro- and microscopic structure of matter, and finally, results in thermodynamic and hydrodynamic equations.
																								



2.
SPACE–TIME SCALES IN THE LAGRANGE THEORY OF THERMAL HYDRODYNAMIC FLUCTUATIONS

T. V. Lokotosh1, N. P. Malomuzh1, K. N. Pankratov2
1I. I. Mechnikov Odessa State National University, Ukraine
2Odessa National Polytechnic University, Institute of International Educational Programs, Ukraine
Keywords: Lagrangian particle, Maxwell relaxation time, molecular self-diffusion coefficient

Abstract >>
The value and temperature dependence of the Maxwell relaxation time of viscous tensions and the Lagrangian particle radius, which are the main space-time scales in the Lagrange theory of thermal hydrodynamic fluctuations, are discussed. These parameters play the key role in the estimations of the relative value of the collective component of the molecular self-diffusion coefficient. Special attention is paid to the consistency of estimates obtained by different methods.
																								



3.
CLUSTER STRUCTURE OF WATER IN ACCORDANCE WITH THE DATA ON DIELECTRIC PERMITTIVITY AND HEAT CAPACITY

N. P. Malomuzh1, V. N. Makhlaichuk1, P. V. Makhlaichuk1, K. N. Pankratov2
1I. I. Mechnikov Odessa National University, Ukraine
2Odessa National Polytechnic University, Institute of International Educational Programs, Ukraine
Keywords: water structure, clusters, dielectric permittivity, heat capacity

Abstract >>
In the work the character of water clusterization in the whole existence domain of its liquid state is discussed: from supercooled states to the critical point. Conclusions about the cluster composition of liquid water are drawn based on the analysis: 1) of the features of dielectric relaxation; 2) character of the temperature dependence of its static dielectric permittivity, and 3) the value and temperature dependence of different contributions to the heat capacity of the system. It is shown that near the water crystallization point tetramers prevail in its structure, with an increase in the temperature trimers start to play the main role, and near the critical point of water dimers become the major associates. At temperatures near the water crystallization point the obtained results well agree with the data on emission and absorption X-ray spectroscopy.
																								



4.
Calculation of the thermodynamic characteristics of the water MONTE CARLO

A.V. Teplukhin
Institute of Mathematical Problems of Biology, Russian Academy of Sciences, Pushchino, Russia
Keywords: water, simulation, Monte Carlo, NpT, parallel computing, REMC

Abstract >>
The Monte Carlo method and parallel computing are used to calculate the thermodynamic properties of water (density, heat capacity, compressibility, thermal expansion coefficient, and static dielectric constant) in a wide range of temperatures (from 70 K to 530 K) at constant (atmospheric) pressure. Four groups of computational experiments are carried out, each for its own model of the water molecule: TIP3P (Jorgensen et al., 1983), SPC/E (Berendsen et al., 1987), TIP4P/2005 (Abascal&Vega, 2005), and TIP5P-E (Rick, 2004). An additional calculation based on the replica exchange method is conducted for the TIP4P/2005 model. A comparison of the calculated properties of water with experimental data suggests that the TIP4P/2005 model can provide highly realistic computer simulation results for water and aqueous solutions.
																								



5.
COLLECTIVE MOTIONS IN COMPUTER MODELS OF WATER. LARGE–SCALE AND LONG-TIME CORRELATIONS

V. P. Voloshin1, G. G. Malenkov2, Yu. I. Naberukhin1,3
1V. V. Voevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk
2A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Moscow
3Novosibirsk State University, Novosibirsk
Keywords: water structure, diffusive motion, collective effects, large-scale correlations, vortices

Abstract >>
Two-particle correlation functions describing the simultaneous motion of a pair of molecules initially separated by a given distance R0 are calculated to study collective effects in the diffusive motion of water molecules in molecular dynamics models. Various types of such functions and their dependences on the interaction potential, temperature, and the number of particles in the model are considered. At short times (of the order of ten picoseconds), these functions exhibit irregular behavior depending on R0. The most nontrivial and unexpected result was the detection of correlations in the displacements of pairs of particles that extend for tens of angstroms and last for hundreds of picoseconds. Such correlations are not observed in the random walk models of noninteracting particles. It is suggested that the observed large-scale correlations reveal the vortex-like motions of the molecules.
																								



6.
ARGON AND WATER

G. G. Malenkov
A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow
Keywords: water, liquid argon, structure, molecular dynamics

Abstract >>
Computer simulation of liquid argon and water has shown that the structural inhomogeneity pattern visualized by coloring their instantaneous structures according to the volumes of the Voronoi polyhedra is the same for both liquids. The dynamics of argon atoms in the cavity of a clathrate hydrate and in liquid water is considered. The argon atoms included in the network of hydrogen bonds in liquid water are involved in concerted motion. As a result of this concerted motion, the distance between two argon atoms can fluctuate around some value for a fairly long time. The environment of argon atoms in a liquid aqueous solution differs significantly from their environment in clathrate hydrates.
																								



7.
SOLVOPHOBIC EFFECTS: QUALITATIVE DETERMINATION AND QUANTITATIVE DESCRIPTION

I. A. Sedov, B. N. Solomonov
Kazan Federal University, Kazan
Keywords: solvophobic effects, self-association, Gibbs free energy, enthalpy

Abstract >>
Solvophobic effects strongly influence the thermodynamic properties of solutions and are one of the driving forces of self-assembly processes of supramolecular structures. However, the generally accepted definition and a quantitative measure of these effects have so far been absent. Based on the analysis of a large set of experimental data on the thermodynamic functions of solvation in various systems, we propose a qualitative criterion allowing us to judge about whether the solvophobic effects are manifested in the solution or not, and also a method to determine their contributions to the thermodynamic functions of solvation. A feature of the solvophobic effect is a violation of the linear relationship between the Gibbs free energy and the enthalpy of solvation, which is fulfilled for the solutions of different compounds in many non-associated solvents. It is shown that in self-associated solvents the solvophobic effect is observed for any dissolved compounds, including well soluble ones, resulting in an increase in the Gibbs energy of solvation. Previously proposed solvophobicity parameters are considered and compared with our results.
																								



8.
CALCULATION OF PARTIAL MOLAR VOLUME AND ITS COMPONENTS FOR MOLECULAR DYNAMICS MODELS OF DILUTE SOLUTIONS

N. N. Medvedev1,2, V. P. Voloshin1, A. V. Kim1, A. V. Anikeenko1, A. Geiger3
1V. V. Voevodskii Institute of Chemical Kinetics and Combustion, Siberian Division, Russian Academy of Sciences, Novosibirsk
2Novosibirsk State University, Novosibirsk
3Technical University of Dortmund, Dortmund, Germany
Keywords: solutions, partial molar volume, intrinsic volume, molecular dynamics simulation, VoronoiDelaunay method

Abstract >>
This paper is a review of our recent computational studies of volumetric characteristics using computer models of dilute solutions. Partial molar volume (PMV) and its components are calculated for simple and complex molecules in water (methane, noble gases, surfactants, polypeptides). Advantages and disadvantages of various computational methods are discussed. It is proposed to use the VoronoiDelaunay technique to determine the reasonable boundary between a solute molecule and solvent molecules and to identify the PMV components related to the molecule, the boundary layer, and the solvent. It is noted that the observed increase in PMV with temperature for large molecules is due to an increase in the volume of voids in the boundary layer, i.e., due to the thermal volume. In this case, the solvent gives a negative contribution to the PMV. In contrast, for simple molecules (methane), the contribution from the solvent is positive and is the main factor in the increase in the PMV, which is associated with a specific change in water structure around a spherical hydrophobic particle outside the boundary layer. For surfactant molecules, the contribution from the solvent changes sign (from negative to positive) with increasing temperature.
																								



9.
MICROSTRUCTURE OF CONCENTRATED SOLUTIONS IN THE WATERLITHIUM NITRATECALCIUM NITRATE TERNARY SYSTEM FROM MOLECULAR DYNAMICS SIMULATIONS

M. I. Averina, A. V. Egorov, V. I. Chizhik
Saint-Petersburg State University, Saint-Petersburg
Keywords: concentrated and multicomponent aqueous solutions, molecular dynamics method, microstructure

Abstract >>
Method of classical molecular dynamics simulated series solutions of the ternary system water—lithium nitratecalcium nitrate . Calculated radial distribution functions for different pairs of atoms , evaluated coordination numbers of cations and analyzed the nature of changes in the composition of the first solvation shells when the ratio of the components in the system being modeled . The article details the first sphere water molecules in solutions of various concentrations. Allocated 8 basic types entourage structure of the water molecule and its main characteristics , evaluated the probability of occurrence of these structures in the ternary system .
																								



10.
TOPOLOGY OF MOLECULAR NANOSTRUCTURES IN LIQUID ALCOHOLS

A. M. Tolmachev, G. O. Khondar, A. V. Kucherov, N. G. Kryuchenkova
Moscow State University, Russia
Keywords: molecular dynamics, alcohols, molecular nanostructures, topology

Abstract >>
A quantitative topological analysis is conducted of the molecular nanostructures of liquid alcohols as a function of temperature. The analysis is necessary to solve the fundamental problem of the theory of solutions: finding the relationship between the macroparameters of liquids and the structure and properties of intermolecular associates. The analysis is performed using the previously proposed MDGT method, which is based on a combination of molecular dynamics calculations and graph theory. The method enables the recognition and saving of all molecular nanostructures observed in each snapshot of the molecular dynamics trajectory, averaging of data for any number of snapshots to present averaged concentrations of associates (dimers, trimers, etc.), and determination of the concentrations and characteristics of isomers (e.g., chains, branched chains, rings, etc.), bond lengths, angles, etc. in each group of associates.
																								



11.
BULK properties of A liquid phase mixture {ETHYLENE GLYCOL+TERT-BUTANOL} in the temperature range 278.15-348.15 K and pressures of 0.1-100 MPa. I. experimental results, EXCESS and partial molar volumes

G. I. Egorov, D. M. Makarov
G. A. Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo
Keywords: ethylene glycol, tert-butanol, high pressure, coefficients of compressibility, excess molar volumes, partial molar volumes

Abstract >>
The densities r and coefficients of compressibility k = ΔV/V0 of a binary mixture {ethylene glycol (1) + tert- butanol (2)} in the temperature range of 278.15-323.15 K and pressures of 0.1-100 MPa over the entire range of compositions of liquid phase state are measured. Found that the coefficients of compressibility k of the mixture increase both with an increase in the concentration of tert- butanol and with a rise in temperature and pressure. The excess molar volumes of the mixture, apparent, partial molar volumes, and limiting partial molar volumes of the components are calculated. It is showed that the excess molar volumes of the mixture are negative and decrease when the pressure increases. The excess molar volumes are described by the Redlich–Kister equation. The partial molar volumes of ethylene glycol sharply decrease in the range of high concentrations of tert- butanol. The dependences of partial molar volumes of ethylene glycol are characterized by the presence of a region of temperature inversion. The “negative compressibility” of the limiting partial volumes of ethylene glycol is revealed.
																								



12.
BULK properties of A liquid phase mixture {ETHYLENE GLYCOL+TERT-BUTANOL} in the temperature range 278.15-348.15 K and pressures of 0.1-100 MPa. II. MOLAR ISOTHERMAL COMPRESSIBILITY, MOLAR ISOBARIC EXPANSIBILITY, thermal pressure coefficient, aNd internal pressure

G. I. Egorov, D. M. Makarov
G. A. Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo
Keywords: ethylene glycol, tert-butanol, high pressure, molar isothermal compressibility, molar isobaric expansibility, thermal pressure coefficient, internal pressure

Abstract >>
Based on the experimental data, the molar isothermal compressibilities, molar isobaric expansibilities, thermal pressure coefficients, internal pressures of a liquid phase mixture {ethylene glycol (1) + tert-butanol (2)} are calculated for a wide spectrum of compositions in the range of pressures of 0.1-100 MPa and temperatures of 278.15-323.15 K. Shown that the dependences of molar isothermal compressibilities KT,m , molar isobaric expansibilities EP,m , and isochoric thermal pressure coefficients b on the mole fraction of tert-butanol in the mixture are characterized by the absence of extrema typical of aqueous systems. The manifestation of negative partial expansibility and negative partial expansibility of ethylene glycol in the mixture is found. The thermal pressure coefficients decrease with an increase in the mole fraction of tert- butanol at all pressures and temperatures. A rise in the pressure increases the thermal pressure coefficient, while a rise in the temperature decreases its value due to a decrease of free space in the mixture. An increase in the concentration of tert- butanol leads to an increase in the negative temperature coefficient of internal pressure ΔPintT, which indicates a weakening of intermolecular interaction at these compositions.
																								



13.
STRUCTURAL AND THERMODYNAMIC PROPERTIES AND INTERMOLECULAR INTERACTIONS IN AQUEOUS AND ACETONITRILE SOLUTIONS OF APROTIC AMIDES

A. M. Zaichikov1, M. A. Krestyaninov2
1Ivanovo State University of Chemistry and Technology, Russia
2G. A. Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
Keywords: internal pressure, intermolecular interactions, structural and thermodynamic properties of solutions, water, acetonitrile, aprotic amides

Abstract >>
The structural and thermodynamic properties are calculated for mixtures of aprotic amides with water and acetonitrile. The simulation approach is used to identify the specific and nonspecific components of the total energy of intermolecular interactions, which are used to calculate the corresponding contributions to the enthalpy of mixing. The negative enthalpies of mixing in the aqueous mixtures are found to be caused not by heterocomponent specific interactions, but by nonspecific ones. The difference in the structural and thermodynamic properties of the aqueous and nonaqueous mixtures of aprotic amides is shown to be largely due to the behavior of the hydrogen bond network of water and the packing of the resulting solutions.
																								



14.
MANIFESTATION OF ION SPECIFICITY IN THE BEHAVIOR OF THE DYNAMIC DIELECTRIC PERMITTIVITY OF AQUEOUS SOLUTIONS OF ALKALI METAL HALIDES

F. M. Shagieva, L. B. Boinovich
A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow
Keywords: aqueous solutions of potassium halides, dispersion of refractive indices, specific ion effect, dynamic dielectric permittivity, effective polarizability

Abstract >>
Dispersions of the refractive index are measured in aqueous solutions of potassium halides at different salt concentrations and temperatures of the solutions. The specific effect of anions on the dynamic dielectric permittivity of the solutions is found. A model is proposed to evaluate the character of changes in the dynamic dielectric permittivity of the solutions and effective dynamic polarizabilities of ions in the solutions based on the data about the dispersion of refractive indices. The role of ion sizes and the character of their interaction with a solvent in the manifestation of specific ion effects are discussed.
																								



15.
X-RAY DIFFRACTION STUDY OF AlSi MELTS

V. P. Kazimirov, A. M. Yakovenko, A. S. Muratov, A. S. Roik, V. È. Sokolskii
National Taras Shevchenko University of Kiev, Ukraine
Keywords: melts, AlSi melt, microheterogeneous structure, X-ray diffraction

Abstract >>
X-ray diffraction is used to study AlSi melts with a content of 0 at.%, 6 at.%, 10 at.%, 18 at.%, 21 at.%, 26 at.%, 35 at.%, 60 at.%, 80 at.%, and 100 at.% Si. The structural factors, atomic distribution curves, and parameters characterizing the immediate environment of atoms in the melts are calculated. The results are described using the microheterogeneous melt structure model near the liquidus temperature. According to the model, the melts contain microgroupings with the statistical atomic distribution that are similar in composition to the Al6%Si melt and liquid silicon microgroupings. High-temperature studies indicate an increase in the structural homogeneity of the melts with increasing temperature due to the progressive metallization of interatomic bonds in the silicon microgroupings.
																								



16.
KINETICS OF THE FORMATION OF LIESEGANG RINGS

V. I. Kuzmin1, A. F. Gadzaov1, D. L. Tytik2, S. A. Busev2, A. A. Revina2, V. V. Vysotskii2
1Moscow State Technical University of Radio Engineering, Electronics, and Automatics, Moscow
2A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow
Keywords: solutions, Liesegang rings, critical points, gels, bound water, magnesium chloride salts, nanoparticles, diffusion equation, anamorphosis, physicochemical periodic processes

Abstract >>
The kinetics of the formation of Liesegang rings is considered and they are classified. The relationship between the position of the propagating diffusion front and the moments of the formation of Liesegang rings is shown. In order to describe the formation processes of the Liesegang rings a generalized model based on the diffusion equation hierarchy is proposed. The kinetics of changes in the dispersed phase sizes at the initial stage of the formation of Liesegang rings is studied.