Ioffe Institute, 26 Polytechnicheskaya, St. Petersburg 194021, Russia.
J Chem Phys. 2017 Jul 7;147(1):014105. doi: 10.1063/1.4991324.
The aim of this paper is to present a method of a direct evaluation of the chemical potential of fluid, liquid, and solid with kinetic Monte Carlo simulation. The method is illustrated with the 12-6 Lennard-Jones (LJ) system over a wide range of density and temperature. A distinctive feature of the methodology used in the present study is imposing an external potential on the elongated simulation box to split the system into two equilibrium phases, one of which is substantially diluted. This technique provides a reliable direct evaluation of the chemical potential of the whole non-uniform system (including that of the uniformly distributed dense phase in the central zone of the box), which, for example, is impossible in simulation of the uniform crystalline phase. The parameters of the vapor-liquid, liquid-solid, and fluid-solid transitions have been reliably determined. The chemical potential and the pressure are defined as thermodynamically consistent functions of density and temperature separately for the liquid and the solid (FCC) phases. It has been shown that in two-phase systems separated by a flat interface, the crystal melting always occurs at equilibrium conditions. It is also proved that in the limit of zero temperature, the specific heat capacity of an LJ crystal at constant volume is exactly 3R (where R is the gas constant) without resorting to harmonic oscillators.
本文旨在提出一种通过动力学蒙特卡罗模拟直接评估流体、液体和固体化学势的方法。该方法通过广泛的密度和温度范围内的 12-6 Lennard-Jones（LJ）系统进行了说明。本研究中使用的方法的一个显著特点是在拉长的模拟盒上施加外部势，将系统分成两个平衡相，其中一个相实质上是稀释的。这种技术提供了对整个非均匀系统（包括盒中心区域中均匀分布的密集相）的化学势的可靠直接评估，例如，在模拟均匀晶体相时是不可能的。已经可靠地确定了汽液、液固和固液转变的参数。化学势和压力被定义为液体和固体（FCC）相的密度和温度的热力学一致函数。已经表明，在由平界面隔开的两相系统中，晶体熔化总是在平衡条件下发生。还证明了在零温度极限下，LJ 晶体的定容比热容在不依赖谐振子的情况下恰好为 3R（其中 R 是气体常数）。
