Pressure derivatives in the classical molecular-dynamics ensemble.
Pressure derivatives in the classical molecular-dynamics ensemble.
复制标题
经典分子动力学系综中的压力导数。
DOI：
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发表时间：
2006
影响因子：
4.4
通讯作者：
S. Kabelac
中科院分区：
文献类型：
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作者：
K. Meier;S. Kabelac
在Lustig [J. Chem.Phys.100，3048（1994）]对分子动力学系综的综合处理的框架中，考虑了在常规分子动力学模拟中热力学状态变量的计算，特别是压力对密度和温度的导数。本文从两个方面改进了Lustig的工作。首先，导出了分子动力学系综中基本相空间函数的一般表达式，其中考虑到力学量G除了是系统的粒子数、体积、能量和总动量之外，还是一个运动常数。G与系统质心的初始位置有关。其次，导出了势能体积导数的正确的一般表达式。后一结果解决了Lustig [J. Chem. Phys. 109，8816（1998）]和Meier [Lennard-Jones Model Fluid（Shaker，亚琛，2002）]报道的问题，并且使得能够正确计算等熵和等温压缩率、声速以及原则上所有较高压力导数。推导出的方程进行了验证，通过计算的几个状态变量和压力导数高达二阶的分子动力学模拟与256个粒子在两个状态点的Lennard-Jones流体在气体和液体区域。它也被发现，这是不可能的系统，这种规模的计算三阶和更高阶的压力导数由于有限的精度的算法，用于整合的运动方程。
The calculation of thermodynamic state variables, particularly derivatives of the pressure with respect to density and temperature, in conventional molecular-dynamics simulations is considered in the frame of the comprehensive treatment of the molecular-dynamics ensemble by Lustig [J. Chem. Phys. 100, 3048 (1994)]. This paper improves the work of Lustig in two aspects. In the first place, a general expression for the basic phase-space functions in the molecular-dynamics ensemble is derived, which takes into account that a mechanical quantity G is, in addition to the number of particles, the volume, the energy, and the total momentum of the system, a constant of motion. G is related to the initial position of the center of mass of the system. Secondly, the correct general expression for volume derivatives of the potential energy is derived. This latter result solves a problem reported by Lustig [J. Chem. Phys. 109, 8816 (1998)] and Meier [Computer Simulation and Interpretation of the Transport Coefficients of the Lennard-Jones Model Fluid (Shaker, Aachen, 2002)] and enables the correct calculation of the isentropic and isothermal compressibilities, the speed of sound, and, in principle, all higher pressure derivatives. The derived equations are verified by calculations of several state variables and pressure derivatives up to second order by molecular-dynamics simulations with 256 particles at two state points of the Lennard-Jones fluid in the gas and liquid regions. It is also found that it is impossible for systems of this size to calculate third- and higher-order pressure derivatives due to the limited accuracy of the algorithm employed to integrate the equations of motion.