I. Yu. Gotlib

Properties of coexisting fluid phases of a binary system methanolethane by computer simulation

Abstract Methaneethane and methanolethane binary mixtures were simulated by the Gibbs ensemble Monte Carlo method. Thermodynamic properties and structural characteristics of coexisting fluid phases were calculated. Reasonable agreement with experiment was obtained, in particular, for the liquid-liquid-vapour coexisting pressure in the methanolethane system at 298.15 K. A lyophobic effect, which affects the phase behaviour and the hydrogen-bonding characteristics of the liquid phase, was observed. In order to improve agreement with experiment, the values of the Lennard-Jones interactions parameters for CH3OH and C2H6 molecules were adjusted.

Molecular Dynamics Simulations of Lix Mn2O4 Spinel Solid Solutions with Simple Potential Models

Molecular dynamics simulations of LixMn2O4 (0 < x ≤ 1) spinel solid solutions were carried out with the use of simple pair potentials available in the literature. The results demonstrate that computer simulations using the existing potentials with an exponential repulsion term fail to adequately reproduce appreciable Li+ mobility in a stable (near-zero mobility of the manganese and oxygen ions) crystalline phase. Lennard-Jones potentials make it possible to simulate such a phase at high temperatures (on the order of 1000 K).

Molecular dynamics simulation of the Ba1−xGdxF2+x system in a wide temperature range

Abstract Internal energy, diffusion coefficients, ion–ion correlation functions, anion density and characteristics of ionic motion in barium gadolinium fluoride (Ba 1− x Gd x F 2+ x , 0 x ≤0.25) were calculated using molecular dynamics simulation. The simulations were performed for a wide range of temperatures, including the temperature of the superionic transition. The simple model interaction potential (Born–Mayer–Huggins model) was used. The calculated thermodynamic and transport properties are in satisfactory agreement with experiment; the discrepancies can be explained by the fact that cluster formation, which occurs in the real crystal, is not taken into account in the simulations. It was found that at x >0.1, both 4 b and 48 i positions in the lattice were relatively favorable for interstitial F − ions. At low dopant concentrations, anion migration in the simulated system takes place mainly by the interstitialcy mechanism with noncollinear hops. The computer experiment confirmed that trigonal Gd 3+ –F − (interstitial) “dipole complexes” are preferable in comparison with tetragonal ones. Existence of the tendency to clustering of gadolinium ions in the simulated system was also confirmed using elements of Monte Carlo technique.

Molecular dynamics simulation of silver bromide nanostructures in single-walled carbon nanotubes

Nanostructures formed upon filling single-walled carbon nanotubes of different diameters (ranging from 11.5 to 17.6 Å) with silver bromide have been investigated using the molecular dynamics method. The results of molecular dynamics computer simulation have demonstrated that, in such tubes, AgBr nanotubes in the form of rolled-up two-dimensional crystalline networks (including structures both with a trigonal coordination and with a tetragonal coordination of ions) can be produced as well as fragments of the NaCltype structure, which is typical of bulk AgBr crystals. In the initial stage of their filling, the carbon nanotubes in the silver bromide melt are deformed, on average, to a greater extent than those in a similar system with AgI. After taking out from the melt, the degree of deformation of the nanotubes decreases and, in the majority of cases, AgBr nanotubular structures based on a hexagonal network are formed inside them.

Molecular Dynamics Simulations of Ba1 – xGdxF2 + x Solid Solutions over a Wide Temperature Range: II. Structural Characteristics and Fluoride Ion Diffusion

The atomic-scale structure (pair correlation functions and anion-density distribution) and fluoride-ion diffusion in Ba1 – xGdxF2 + x solid solutions are investigated over a wide temperature range, including the superionic transition, by molecular dynamics simulations with Born–Mayer–Huggins pair potentials. According to the simulation results for x > 0.1, both the 4b(cubic site symmetry) and 48i positions accommodate fluorine interstitials (F–i). Below the superionic transition, the migration of F– ions at low doping levels is dominated by noncollinear jumps between lattice and interstitial sites. Computer simulations confirm that trigonal Gd3+–F–i dipolar complexes prevail over tetragonal complexes. It is shown using elements of Monte Carlo simulation that the rare-earth ions in the solid solutions have a tendency to aggregate.

Computer simulation of AgI nanostructures in single-wall carbon nanotubes

Nanostructures resulting from the incorporation of silver iodide into single-wall carbon nanotubes (SWCNTs) of various diameters have been studied using molecular dynamics simulation. The results indicate the formation of single-wall silver iodide nanotubes when the SWCNT diameter is within 14.2 Å, whereas thicker carbon tubes contain, in addition, an axial “filament” of silver and iodide ions. AgI nanotubes in SWCNTs typically have a hexagonal structure (with the ions in trigonal coordination).

Molecular Dynamics Simulations of Ba1 – xGdxF2 + xSolid Solutions over a Wide Temperature Range: I. Thermodynamic and Transport Properties

The internal energy and transport properties of Ba1 – xGdxF2 + xsolid solutions are investigated over a wide temperature range, including the superionic transition, by molecular dynamics simulations with Born–Mayer–Huggins pair potentials. The simulation results are in reasonable agreement with available experimental data.

Molecular dynamics simulation of SnF2 nanostructures in the internal channels of single-walled carbon nanotubes

A molecular dynamics simulation of solid tin(II) fluoride nanostructures formed in internal channels of single-walled carbon nanotubes (SWCNTs) has been performed using two types of model potentials—without and with inclusion of the polarization of ions. For the potential taking into account the polarization of ions, an ordered SnF2@SWCNT structure is reproduced: in SWCNT(10, 10), it has the form of the SnF2 internal nanotube. At the same time, the SnF2@SWCNT(11,11) structure is substantially disordered (glass-like). It has been found that heating of the SnF2@SWCNT model system produces a superionic state characterized by a high mobility of fluorine ions without migration of tin ions. The model potentials disregard the covalent character of Sn-F bonds and the specific interactions of a lone electron pair of the Sn2+ ion. This makes it impossible to completely reproduce the properties of SnF2 at normal pressures. However, some characteristics of the SnF2 high-pressure modification can be reproduced if the polarization of ions is taken into account.

Molecular dynamic simulation of polymer and polymer-oxide nanoclusters

Small systems composed of 10 molecules of poly-p-xylylene or a TiO2 cluster (rutile) surrounded by 10 molecules of poly-p-xylylene are modeled via the method of molecular dynamics. The thermodynamic characteristics, structure, and mobility of poly-p-xylylene chains in the model systems are studied in a wide temperature interval (195–995 K) and compared with the corresponding characteristics of a volume phase and an individual polymer chain. With increasing temperature, the mobility of monomer units increases; this process leads to disordering. At high temperatures, there is an evident tendency for loosening and further disintegration of an aggregate into individual chains, which adopt a Gaussian coil shape. These transitions are similar to the transitions of the folded individual molecule of poly-p-xylylene. Introduction of a TiO2 nanoparticle into poly-p-xylylene has a strong effect on the characteristics of the system with short polymer chains, where the adhesion of poly-p-xylylene molecules on the TiO2 surface is accompanied by disordering in the peripheral region.