Quantum fluctuations and isotope effects in ab initio descriptions of water

TL;DR

This paper uses advanced ab initio simulations to explore how nuclear quantum effects influence water's structure and isotope behavior, providing insights aligned with recent experimental findings.

Contribution

It presents a fully ab initio approach that simultaneously accounts for nuclear and electronic quantum effects in water, clarifying their interplay.

Findings

Quantum kinetic energies of particles measured

Free energy change upon isotope exchange quantified

Isotope fractionation ratio accurately predicted

Abstract

Nuclear quantum effects, such as zero-point energy and tunneling, cause significant changes to the structure and dynamics of hydrogen bonded systems such as liquid water. However, due to the current inability to simulate liquid water using an exact description of its electronic structure, the interplay between nuclear and electronic quantum effects remains unclear. Here we use simulations that incorporate the quantum mechanical nature of both the nuclei and electrons to provide a fully ab initio determination of the particle quantum kinetic energies, free energy change upon exchanging hydrogen for deuterium and the isotope fractionation ratio in water. These properties, which selectively probe the quantum nature of the nuclear degrees of freedom, allow us to make direct comparison to recent experiments and elucidate how electronic exchange and correlation and nuclear quantum fluctuations determine the structure of the hydrogen bond in water.