Distributed Charge Models of Liquid Methane and Ethane for Dielectric Effects and Solvation

TL;DR

This paper introduces fixed-charge, non-polarizable models for liquid methane and ethane that incorporate fixed molecular dipoles to accurately reproduce dielectric constants, enabling better simulation of solvation and dielectric effects.

Contribution

The authors develop a novel fixed-charge model with broken charge symmetry to simulate dielectric effects in liquid hydrocarbons, improving upon traditional symmetric models.

Findings

Models reproduce experimental dielectric constants.

Enhanced solvation of ions and water molecules.

Fixed-dipole models outperform dipole-free models.

Abstract

Liquid hydrocarbons are often modeled with fixed, symmetric, atom-centered charge distributions and Lennard-Jones interaction potentials that reproduce many properties of the bulk liquid. While useful for a wide variety of applications, such models cannot capture dielectric effects important in solvation, self-assembly, and reactivity. The dielectric constants of hydrocarbons, such as methane and ethane, physically arise from electronic polarization fluctuations induced by the fluctuating liquid environment. In this work, we present non-polarizable, fixed-charge models of methane and ethane that break the charge symmetry of the molecule to create fixed molecular dipoles, the fluctuations of which reproduce the experimental dielectric constant. These models can be considered a mean-field-like approximation that can be used to include dielectric effects in large-scale molecular simulations of polar and charged molecules in liquid methane and ethane. We further demonstrate that solvation of model ionic solutes and a water molecule in these fixed-dipole models improve upon dipole-free models.