An ab initio supercell approach for high-harmonic generation in liquids

TL;DR

This paper introduces an ab initio supercell method combining molecular dynamics and real-time density functional theory to predict high-harmonic generation in liquids, exemplified on water, accounting for structural disorder and ultrafast nuclear dynamics.

Contribution

It presents a novel, practical ab initio approach for modeling high-harmonic generation in liquids, adaptable to various amorphous systems and including nuclear motion effects.

Findings

Harmonic emission varies with structural order in water.

Ultrafast nuclear dynamics influence non-linear optical response.

Method provides converged, realistic predictions for liquids.

Abstract

Many important ultrafast phenomena take place in the liquid phase. However, there is no practical theory to predict how liquids respond to intense light. Here, we propose an $ab~initio$ accurate method to study the non-perturbative interaction of intense pulses with a liquid target to investigate its high-harmonic emission. We consider the case of liquid water, but the method can be applied to any other liquid or amorphous system. The liquid water structure is reproduced using Car-Parrinello molecular dynamics simulations in a periodic supercell. Then, we employ real-time time-dependent density functional theory to evaluate the light-liquid interaction. We outline the practical numerical conditions to obtain a converged response. Also, we discuss the impact of nuclei ultrafast dynamics on the non-linear response of system. In addition, by considering two different ordered structures of ice, we show how harmonic emission responds to the loss of long-range order in liquid water.