Nuclear Quantum Effects on the Electronic Structure of Water and Ice

TL;DR

This study investigates how nuclear quantum effects influence the electronic properties of water and ice, revealing that quantum fluctuations significantly alter their electronic gaps and proton delocalization, aligning theoretical results with experimental data.

Contribution

It introduces a combined machine-learning and many-body perturbation approach to quantify nuclear quantum effects on water and ice's electronic structure at finite temperatures.

Findings

Nuclear quantum effects increase the fundamental gap of ice more than water.

Quantum fluctuations lead to greater proton delocalization in ice.

Results align with experimental estimates of electronic gaps.

Abstract

The electronic properties and optical response of ice and water are intricately shaped by their molecular structure, including the quantum mechanical nature of hydrogen atoms. In spite of numerous studies appeared over decades, a comprehensive understanding of the effect of the nuclear quantum motion on the electronic structure of water and ice at finite temperatures remains elusive. Here, we utilize molecular simulations that harness the efficiency of machine-learning potentials and many-body perturbation theory to assess the impact of nuclear quantum effects on the electronic structure of water and hexagonal ice. By comparing the results of path-integral and classical simulations, we find that including nuclear quantum effects leads to a larger renormalization of the fundamental gap of ice, compared to that of water, eventually leading to a comparable gap in the two systems, consistent with experimental estimates. Our calculations suggest that the quantum fluctuations responsible for an increased delocalization of protons in ice, relative to water, are a key factor leading to the enhancement of nuclear quantum effects on the electronic structure of ice.