Truncation Effects of Shift Function Methods in Bulk Water Systems

Kazuaki Takahashi

doi:10.3390/e15083339

Abstract

A reduction of the cost for long-range interaction calculation is essential for large-scale molecular systems that contain a lot of point charges. Cutoff methods are often used to reduce the cost of long-range interaction calculations. Molecular dynamics (MD) simulations can be accelerated by using cutoff methods; however, simple truncation or approximation of long-range interactions often offers serious defects for various systems. For example, thermodynamical properties of polar molecular systems are strongly affected by the treatment of the Coulombic interactions and may lead to unphysical results. To assess the truncation effect of some cutoff methods that are categorized as the shift function method, MD simulations for bulk water systems were performed. The results reflect two main factors, i.e., the treatment of cutoff boundary conditions and the presence/absence of the theoretical background for the long-range approximation.

Highlights

In the calculation of thermodynamic, structural and dynamical properties by molecular dynamics (MD) simulations, the effect of long-range interactions is an important issue
The thermodynamic properties for the shift function methods and Ewald sum were calculated by potential energies
The fastest decline was observed in the case of linearcombination-based IPS (LIPS)-fifth; the error was roughly in proportion to rc−4

Summary

Introduction

In the calculation of thermodynamic, structural and dynamical properties by molecular dynamics (MD) simulations, the effect of long-range interactions is an important issue. Long-range interactions on the periodic boundary conditions (PBCs) can be calculated using the Ewald sum or cutoff methods. The. Ewald sum [1] is the key standard method used in calculations involving long-range interactions with the periodic boundary condition. Ewald sum [1] is the key standard method used in calculations involving long-range interactions with the periodic boundary condition In this method, the total energy is split into real and reciprocal space. Some reports on the accuracy of the IPS method of homogeneous [48,50,51,52,53,54] and heterogeneous systems [47,50,55,56,57] show that the method yields estimates in good agreement with the results of the Ewald sum. The results reflect two main factors, i.e., the treatment of cutoff boundary conditions and the presence/absence of the theoretical background for long-range approximation

Experimental

Potential Energy

Self-Diffusion Coefficient

Radial Distribution Function

Dipole-Dipole Correlation

Conclusions