Polarizable Multipolar Molecular Dynamics Using Distributed Point Charges

TL;DR

This paper introduces distributed point charge models (DCM) and their minimal and polarizable variants, enhancing electrostatic modeling in molecular dynamics with improved accuracy, speed, and compatibility with existing force fields.

Contribution

The work develops systematic approaches for reducing fitting errors, speeds up the fitting process for larger molecules, and introduces polarizable DCMs, broadening their applicability in condensed-phase simulations.

Findings

DCMs retain the accuracy of original models in electrostatic calculations.

The new methods significantly speed up the fitting process for large molecules.

Polarizable DCMs effectively model electrostatics in various force fields.

Abstract

Distributed point charge models (DCM) and their minimal variants (MDCM) have been integrated with tools widely used for condensed-phase simulations, including a virial-based barostat and a slow-growth algorithm for thermodynamic integration. Minimal DCM is further developed with a systematic approach to reduce fitting errors in the electrostatic interaction energy and a new fragment-based approach offers considerable speedup of the MDCM fitting process for larger molecules with increased numbers of off-centered charged sites. Finally, polarizable (M)DCM is also introduced in the present work. The developments are used in condensed-phase simulations of popular force fields with commonly applied simulation conditions. (M)DCM equivalents for a range of widely used water force fields and for fluorobenzene (PhF) are developed and applied along with the original models to evaluate the impact of reformulating the electrostatic term. Comparisons of the molecular electrostatic potential (MEP), electrostatic interaction energies, and bulk properties from molecular dynamics simulations for a range of models from simple TIP$n$P ($n = 3-5$) to the polarizable, multipolar iAMOEBA models for water and an existing quadrupolar model for PhF confirm that DCMs retain the accuracy of the original models, providing a homogeneous, efficient, and generic point charge alternative to a multipolar electrostatic model for force field development and multilevel simulations.