LJ势氩系统分子动力学模拟中截断半径的选择

Application of cutoff distance selection in molecular dynamics simulation of LJ argon system

近年来在分子动力学方法研究LJ(Lennard-Jones)势氩系统时,越来越多的计算建议采用4.5σ甚至更大的截断半径(σ为氩原子直径)。本工作研究了不同截断半径对等温等压NPT系综氩系统熔沸点相图的影响,分析了不同截断半径下在氩系统的熔点及液相区域不同热力学状态点的径向分布函数和速度自相关函数。结果表明,以熔点为基准,在距离其相同液态温区分率的热力学温度点能获得相同的热力学性质,2.5σ的截断半径在模拟的准确性和计算性能上均能满足模拟的要求,本工作为液氩模拟中截断半径的选择指明了一个新的思考方向。

In Lennard-Jones(LJ)potential argon system investigated by molecular dynamics simulation,the different cutoff distances are frequently applied to calculate the interactive force between atoms,and some reports have given out the influence of the cutoff distances on the simulation systems.More and more calculations suggest to use 4.5?or even larger truncation distances(?is the diameter of argon atom)to obtain the more accurate thermodynamic properties of the systems.In this work,a simple method was proposed to solve the problem of superheating encountered in the calculation of melting point by direct heating,where an independent track and ensemble at each temperature point are run.And then,the effect of different cutoff distances on the phase diagrams of the melting and boiling points of argon system in the NPT ensemble was studied.The melting point was in good agreement with the experimental and theoretically calculated values when the cutoff distance of 2.5?was used.However,the deviation from the experimental melting point became more evident when the larger cutoff distances were employed.In order to find out the underlying mechanism behind the deviation,the radial distribution functions and velocity autocorrelation function at the melting points and different thermodynamic states of the liquid argon with different cutoff distances were analyzed.It was found that the same thermodynamic properties can be obtained at the corresponding thermodynamic state points under different truncation distances.The mapping between the different thermodynamic state points was understandable due to the different thermodynamic states at the same temperatures under the varied truncation distances,and was beneficial to significantly reduce the computational workload at the smaller cutoff distance.This work proposed an exploratory way for the selection of the cutoff distance in the simulation of liquid argon,where the truncation distance of 2.5?can meet the requirements of computational accuracy and performance in the simulations.