Dielectric properties of water inside charged nanoslits: A comparison of rigid and flexible three site models

Abstract

Water confined inside charged nanoslits serves as a minimal model for a nanocapacitor. This charged system is not only interesting for practical applications of nanocapacitors but also for understanding how the charged wall and electric field modify the structure of water and how these modifications reflect in the fluid behavior. Specially, water behavior under nanoconfinement differs drastically from that observed in bulk, with distinct structural, dynamic, and dielectric properties. In recent years, classical atomistic models have been extensively employed to understand this behavior. Among them, three-site models are an attractive class due to their simplicity, allowing large-scale and long-time simulations. In this work, the behavior of water inside a charged nanoslit of graphene is analyzed to study the water molecules under electrical confinement, polarizing the nanoslit of graphene and creating an electric field inside the nanopore. The dipole moment, static dielectric constant, infrared spectrum, and diffusion of water are analyzed through molecular structure under this type of electrical confinement with two force fields of water. The three-site water models used here are the SPC/ϵ and the FAB/ϵ, with the former being a rigid model that improves upon the SPC model, and the latter being a flexible model that improves all the force fields of three-site non-polarizable and flexible models. Our findings show that, although both models can reproduce the low dielectric constant of water near interfaces, the total dipole moment and polarization factor are affected by the model's flexibility.