Interplay of local hydrogen-bonding and long-ranged dipolar forces in simulations of confined water

TL;DR

This paper demonstrates how Local Molecular Field (LMF) theory effectively corrects the inaccuracies caused by spherical Coulomb interaction truncations in simulations of confined water, improving electrostatic property predictions.

Contribution

The study applies LMF theory to various confined water systems, showing its ability to correct truncation errors and enhance understanding of hydrogen bonding and electrostatics interplay.

Findings

LMF theory corrects truncation errors in confined water simulations.

Spherical truncations fail significantly in systems with electric fields.

LMF provides intuitive insights into hydrogen bonding and electrostatics balance.

Abstract

Spherical truncations of Coulomb interactions in standard models for water permit efficient molecular simulations and can give remarkably accurate results for the structure of the uniform liquid. However truncations are known to produce significant errors in nonuniform systems, particularly for electrostatic properties. Local molecular field (LMF) theory corrects such truncations by use of an effective or restructured electrostatic potential that accounts for effects of the remaining long-ranged interactions through a density-weighted mean field average and satisfies a modified Poisson's equation defined with a Gaussian-smoothed charge density. We apply LMF theory to three simple molecular systems that exhibit different aspects of the failure of a naive application of spherical truncations -- water confined between hydrophobic walls, water confined between atomically-corrugated hydrophilic walls, and water confined between hydrophobic walls with an applied electric field. Spherical truncations of 1/r fail spectacularly for the final system in particular, and LMF theory corrects the failings for all three. Further, LMF theory provides a more intuitive way to understand the balance between local hydrogen bonding and longer-ranged electrostatics in molecular simulations involving water.