Tunneling and delocalization in hydrogen bonded systems: a study in position and momentum space

TL;DR

This study uses advanced molecular dynamics to analyze proton momentum distributions in high-pressure ice phases, revealing tunneling signatures and delocalization effects consistent with experimental observations.

Contribution

It applies a novel open path integral Car-Parrinello molecular dynamics method to investigate quantum tunneling and delocalization in hydrogen bonded ice phases under high pressure.

Findings

Symmetric hydrogen bonds show narrowed momentum distributions.

Tunneling signatures include a low-to-intermediate momentum narrowing and extended tails.

Results align with recent experimental data on confined water.

Abstract

Novel experimental and computational studies have uncovered the proton momentum distribution in hydrogen bonded systems. In this work, we utilize recently developed open path integral Car-Parrinello molecular dynamics methodology in order to study the momentum distribution in phases of high pressure ice. Some of these phases exhibit symmetric hydrogen bonds and quantum tunneling. We find that the symmetric hydrogen bonded phase possesses a narrowed momentum distribution as compared with a covalently bonded phase, in agreement with recent experimental findings. The signatures of tunneling that we observe are a narrowed distribution in the low-to-intermediate momentum region, with a tail that extends to match the result of the covalently bonded state. The transition to tunneling behavior shows similarity to features observed in recent experiments performed on confined water. We corroborate our ice simulations with a study of a particle in a model one-dimensional double well potential that mimics some of the effects observed in bulk simulations. The temperature dependence of the momentum distribution in the one-dimensional model allows for the differentiation between ground state and mixed state tunneling effects.