High-Temperature Collision Integrals for m-6-8 and Hulburt–Hirschfelder Potentials

This study is aimed to determine collision integrals for atoms interacting according to the m-6-8 and Hulburt–Hirschfelder potentials and analyze the differences between potentials. The precision of four significant digits was reached at all tested temperatures, and for high-temperature applications, six digits were calculated. The proposed method was tested on the Lennard-Jones potential and found to excellently agree with the recent high-quality data. In addition, the Hulburt–Hirschfelder potential was used for determining the collision integrals of the interaction of nitrogen atoms in the ground electronic state and compared with other known values. The calculations were performed using Mathematica computation system which can deal with singularities (so-called orbiting).

Bulk phase behavior and interfacial properties of binary mixtures of Lennard-Jones chains and solvent: a Density Functional Theory Study

A Density Functional Theory study is performed to analyze both bulk and interfacial properties of solvent-polymer binary mixtures. The effects of increasing polymer chain length on the bulk phase diagram...

Weighted L 2-contractivity of Langevin dynamics with singular potentials

Convergence to equilibrium of underdamped Langevin dynamics is studied under general assumptions on the potential U allowing for singularities. By modifying the direct approach to convergence in L 2 pioneered by Hérau and developed by Dolbeault et al, we show that the dynamics converges exponentially fast to equilibrium in the topologies L 2(dμ) and L 2(W* dμ), where μ denotes the invariant probability measure and W* is a suitable Lyapunov weight. In both norms, we make precise how the exponential convergence rate depends on the friction parameter γ in Langevin dynamics, by providing a lower bound scaling as min(γ, γ −1). The results hold for usual polynomial-type potentials as well as potentials with singularities such as those arising from pairwise Lennard-Jones interactions between particles.

Classical density functional approach to depletion interaction of Lennard-Jones binary mixtures

In this article, we apply classical density functional theory to investigate the characteristics of depletion interaction in Lennard-Jones (LJ) binary fluid mixtures. First of all, in order to confirm the validity of our adopted density functional formalism, we calculate the radial distribution functions with theoretical approach and compare them with results obtained by molecular dynamics simu- lation. Then this approach is applied to the case of two colloids immersed in LJ solvent systems. We investigate the variation of depletion interaction with respect to the distance of two colloids in LJ binary systems. We find that depletion interaction may be attractive or repulsive, mostly depending on the bulk density of solvent and the temperature of binary system. For high bulk densities, the repulsive barrier of depletion force is remarkable when the total excluded volume of colloids touches each other and reaches a maximum. The height of repulsive barrier is related to the parameters of LJ potential and bulk density. Moreover, depletion force may exhibit attractive wells if the bulk density of solvent is low. The attractive well tends to appear when the surface-surface distance of colloids is half of the size of polymer and deepen with temperature lowering in a fixed bulk density. In contrast with the hard-spheres system, no oscillation of depletion potential around zero is observed.

Thermodynamic Scaling of the Shear Viscosity of Lennard-Jones Chains of Variable Rigidity

In this work, the thermodynamic scaling framework has been used to emphasize the limitations of fully flexible coarse grained molecular models to yield shear viscosity of real liquids. In particular, extensive molecular dynamics simulations have confirmed that, while being reasonable to describe the viscosity of short normal alkanes, the fully flexible Lennard-Jones and Mie chains force fields are inadequate to capture the density dependence of shear viscosity of medium to long alkanes. In addition, it is shown that such a weakness in terms of coarse grained molecular models can be readily quantified by using the thermodynamic scaling framework. As a simple alternative to these force fields, it is demonstrated that the insertion of a variable intramolecular rigidity in the Lennard-Jones chains model exhibits promising results to model medium to long chain-like real fluids from both thermodynamic and viscosity points of view.

Molecular diffusion in gases and liquids

The diffusion coefficients in gases and liquids calculated by the molecular dynamics method with the use of the hard absolutely rough elastic spheres model are compared with those calculated using the Lennard-Jones potential. It is shown that dependences of reduced diffusion coefficients on density are similar, but differ numerically for different intermolecular interaction models. The simulation results have been compared with the experimental data on the diffusion in gaseous and liquid argon and in liquid benzene.