Different computational techniques in combination with molecular dynamics computer simulation are used to to determine the wall-liquid and the wall-crystal interfacial free energies of a modified Lennard-Jones (LJ) system in contact with a solid wall. Two different kinds of solid walls are considered: a flat structureless wall and a structured wall consisting of an ideal crystal with the particles rigidly attached to fcc lattice sites. Interfacial free energies are determined by a thermodynamic integration scheme, the anisotropy of the pressure tensor, the non-equilibrium work method based on Bennett acceptance criteria, and a method using Cahn's adsorption equations based on the interfacial thermodynamics of Gibbs. For the flat wall, interfacial free energies as a function of different densities of the LJ liquid and as a function of temperature along the coexistence curve are calculated. In case of a structured wall, the interaction strength between the wall and the LJ system and the lattice constant of the structured wall are varied. Using the values of the wall-liquid and wall-crystal interfacial energies along with the value for the crystal-liquid interfacial free energy determined previously for the same system by the "cleaving potential method", we obtain the contact angle as a function of various parameters; in particular the conditions are found under which partial wetting occurs.
In a recent paper [S. Khrapak, Molecules {\bf 25}, 3498 (2000)] the longitudinal and transverse sound velocities of conventional Lennard-Jones systems at the liquid-solid coexistence were calculated. It was shown that the sound velocities remain almost invariant along the liquid-solid coexistence boundary lines and that their magnitudes are comparable with those of repulsive soft sphere and hard sphere models at the fluid-solid phase transition. This implies that attraction does not affect the magnitude of sound velocities at the fluid-solid phase transition. This paper provides further eviden…
This paper studies physical aging by computer simulations of a 2:1 Kob-Andersen binary Lennard-Jones mixture, a system that is less prone to crystallization than the standard 4:1 composition. Starting from thermal-equilibrium states, the time evolution of the following four quantities is monitored following up and down jumps in temperature: the potential energy, the virial, the average squared force, and the Laplacian of the potential energy. Despite the fact that significantly larger temperature jumps are studied here than in previous experiments, to a good approximation all four quantities c…
It is demonstrated that the crossover between gas- and liquid-like regions on the phase diagram of the Lennard-Jones system occurs at a fixed value of the density divided by its value at the freezing point, $ρ/ρ_{\rm fr}\simeq 0.35$. This definition is consistent with other definitions proposed recently. As a result a very simple practical expression for the gas-to-liquid crossover line emerges.
Liquids displaying strong virial-potential energy correlations conform to an approximate density scaling of their structural and dynamical observables. This scaling property does not extend to the entire phase diagram, in general. The validity of the scaling can be quantified by a correlation coefficient. In this work a simple scheme to predict the correlation coefficient and the density-scaling exponent is presented. Although this scheme is exact only in the dilute gas regime or in high dimension d, a comparison with results from molecular dynamics simulations in d = 1 to 4 shows that it repr…
Longitudinal and transverse sound velocities of Lennard-Jones systems are calculated at the liquid-solid coexistence using the additivity principle. The results are shown to agree well with the ``exact'' values obtained from their relations to excess energy and pressure. Some consequences, in particular, in the context of the Lindemann's melting rule and Stokes-Einstein relation between the self-diffusion and viscosity coefficients are discussed. Comparison with available experimental data on the sound velocities of solid argon at melting conditions is provided.
讨论了一维链平衡态中断裂和团簇的定义。解析表达式获得预期的集群长度，$\langle K \rangle$，作为温度和压力的函数，在一个一维的Lennard-Jones链。这些表达式进行了比较，从分子动力学模拟的结果。发现$\langle K \rangle$随$β= 1/k_BT$和压力呈指数增加，$P$与文献中以前的结果一致。说明了一种使用$\langle K \rangle (β, P)$生成Lennard-Jones链的“相图”的方法。讨论了Lennard-Jones链中热输运研究的一些意义。
How universal is the Lindemann criteria in melting of Lennard-Jones polydisperse solids?
通常认为，当结晶固体颗粒的均方位移（MSD）超过阈值时发生熔融。这被称为林德曼标准，由林德曼于1910年首次提出。然而，Chakravarty等人证明了这种常识是不充分的，因为当压力也允许沿着相图的共存线变化时，熔融时的MSD可能是温度依赖性的[Chakravarty C，Debenedetti PG和Stillinger F H 2007 J.Chem.Phys.126 204508]。本文通过对二维和三维多分散Lennard-Jones固体的广泛的分子动力学模拟表明，在熔融时，粒度分布的小极限和大极限上的颗粒表现出显著不同的林德曼比。尽管MSD中存在所有分散体，但发现在尺寸分散度为5-10%时，熔融在两个维度上都是一级的。
It is demonstrated that properly reduced transport coefficients (self-diffusion, shear viscosity, and thermal conductivity) of Lennard-Jones fluids along isotherms exhibit quasi-universal scaling on the density divided by its value at the freezing point. Moreover, this scaling is closely related to the density scaling of transport coefficients of hard-sphere fluids. The Stokes-Einstein relation without the hydrodynamic diameter is valid in the dense fluid regime. The lower density boundary of its validity can serve as a practical demarcation line between gas-like and liquid-like regimes.
Unlike crystalline solids or ideal gases, transport properties remain difficult to describe from a microscopic point of view in liquids, whose dynamics result from complex energetic and entropic contributions at the atomic scale. Two scenarios are generally proposed: one represents the dynamics in a fluid as a series of energy barrier crossings, leading to Arrhenius-like laws, while the other assumes that atoms rearrange themselves by collisions, as exemplified by the free volume model. To assess the validity of these two views, we computed, using molecular dynamics simulations, the transport …
