Hammonds K D, Heyes D M
Cambridge, United Kingdom.
Department of Physics, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom.
J Chem Phys. 2022 Aug 21;157(7):074108. doi: 10.1063/5.0101450.
Practical implementations of the Ewald method used to compute Coulomb interactions in molecular dynamics simulations are hampered by the requirement to truncate its reciprocal space series. It is shown that this can be mitigated by representing the contributions from the neglected reciprocal lattice vector terms as a simple modification of the real space expression in which the real and reciprocal space series have slightly different charge spreading parameters. This procedure, called the α' method, enables significantly fewer reciprocal lattice vectors to be taken than is currently typical for Ewald, with negligible additional computational cost, which is validated on model systems representing different classes of charged system, a CsI crystal and melt, water, and a room temperature ionic liquid. A procedure for computing accurate energies and forces based on a periodic sampling of an additional number of reciprocal lattice vectors is also proposed and validated by the simulations. The convergence characteristics of expressions for the pressure based on the forces and the potential energy are compared, which is a useful assessment of the accuracy of the simulations in reproducing the Coulomb interaction. The techniques developed in this work can reduce significantly the total computer simulation times for medium sized charged systems, by factors of up to ∼5 for those in the classes studied here.
用于分子动力学模拟中计算库仑相互作用的埃瓦尔德方法的实际应用，因截断其倒易空间级数的要求而受到阻碍。结果表明，通过将被忽略的倒易晶格矢量项的贡献表示为实空间表达式的一种简单修正，可以缓解这一问题，其中实空间和倒易空间级数具有略有不同的电荷扩散参数。这个过程称为α'方法，与目前埃瓦尔德方法通常采用的情况相比，它能够采用显著更少的倒易晶格矢量，而额外的计算成本可以忽略不计，这在代表不同类型带电系统的模型体系（碘化铯晶体和熔体、水以及室温离子液体）上得到了验证。还提出了一种基于对额外数量的倒易晶格矢量进行周期性采样来计算精确能量和力的方法，并通过模拟进行了验证。比较了基于力和势能的压力表达式的收敛特性，这对于评估模拟在再现库仑相互作用方面的准确性是一种有用的评估。这项工作中开发的技术可以显著减少中等规模带电系统的总计算机模拟时间，对于这里研究的那些系统，减少倍数可达约5倍。
