Accurate Thermodynamics for Short-Ranged Truncations of Coulomb Interactions in Site-Site Molecular Models

TL;DR

This paper develops analytical corrections for thermodynamic inaccuracies caused by spherical truncations of Coulomb interactions in molecular simulations, improving the accuracy of properties like energy, pressure, and density.

Contribution

It introduces simple, exact correction methods for thermodynamics in truncated Coulomb systems, extending previous theories to mixtures of flexible molecules.

Findings

Corrected energy and pressure of truncated SPC/E water using second-moment conditions.

Pressure correction as external pressure eliminates density errors in NPT simulations.

Analytical corrections improve thermodynamic accuracy in spherical truncation models.

Abstract

Coulomb interactions are present in a wide variety of all-atom force fields. Spherical truncations of these interactions permit fast simulations but are problematic due to their incorrect thermodynamics. Herein we demonstrate that simple analytical corrections for the thermodynamics of uniform truncated systems are possible. In particular results for the SPC/E water model treated with spherically-truncated Coulomb interactions suggested by local molecular field theory [Proc. Nat. Acad. Sci. USA 105, 19136 (2008)] are presented. We extend results developed by Chandler [J. Chem. Phys. 65, 2925 (1976)] so that we may treat the thermodynamics of mixtures of flexible charged and uncharged molecules simulated with spherical truncations. We show that the energy and pressure of spherically-truncated bulk SPC/E water are easily corrected using exact second-moment-like conditions on long-ranged structure. Furthermore, applying the pressure correction as an external pressure removes the density errors observed by other research groups in NPT simulations of spherically-truncated bulk species.