Ab initio validation on the connection between atomistic and hydrodynamic description to unravel the ion dynamics of warm dense matter

Qiyu Zeng,Dongdong Kang,Xiaoxiang Yu,Shen Zhang,Yunpeng Yao,Jiayu Dai,Bo Chen,Han Wang,Tianyu Gao

doi:10.1103/physrevresearch.3.033116

Abstract

Ion dynamics exhibits inherent multiscale characteristics because it contains both atomistic and hydrodynamic behaviors. Although atomic-scale ab initio molecular dynamics is the subject of intense research on warm dense matter, the macroscopic relaxation process contained in the zero-frequency mode of the ionic dynamic structure factor (DSF) cannot be demonstrated due to the limitation of simulation sizes. Here, we fill this gap via the machine-learning deep potential method. To capture the ion dynamics near the hydrodynamic limit with ab initio accuracy, an accurate and efficient electron-temperature-dependent interatomic potential was constructed. We quantitatively verify the consistency of thermal diffusivities obtained from hydrodynamics and the fluctuation-dissipation theorem and further provide a microscopic perspective of energy transport to understand the zero-frequency mode of DSF. As implemented in two temperature states, a competitive mechanism is found to account for the damping of the zero-frequency mode.

Highlights

INTRODUCTIONThe ion-ion dynamic structure factor (DSF), known as the power spectrum of the reciprocal-space Van Hove function (density-density time correlation function) [1], describes the relaxation and propagation processes spanning different spatial scales
The ion-ion dynamic structure factor (DSF), known as the power spectrum of the reciprocal-space Van Hove function [1], describes the relaxation and propagation processes spanning different spatial scales
Atomic-scale ab initio molecular dynamics is the subject of intense research on warm dense matter, the macroscopic relaxation process contained in the zero-frequency mode of the ionic dynamic structure factor (DSF) cannot be demonstrated due to the limitation of simulation sizes

Summary

INTRODUCTION

The ion-ion dynamic structure factor (DSF), known as the power spectrum of the reciprocal-space Van Hove function (density-density time correlation function) [1], describes the relaxation and propagation processes spanning different spatial scales. Within the framework of classical hydrodynamics, it demonstrates that the DSF consists of three eigenmodes, expressed in terms of phenomenological macroscopic transport coefficients, namely, the two sound waves propagating in opposite directions and one relaxing thermally diffusive mode, defined as. The underlying connection between the microscopic dynamics and the macroscopic transport coefficients can provide a new path to extract the basic physics contained in the ZFM. Thermal diffusivity, a transport coefficient related to the energy and mass transport, serves as the key quantity in the multiscale framework to understand the ZFM. We quantitatively verify the consistency of the thermal diffusivity obtained from the hydrodynamic description and the fluctuation-dissipation theorem; the latter represents microscopic dynamics with a very large wavelength (small wave number). We analyze the single-particle diffusional motion and collective motion, which both contribute to the ZFM in DSF, and we elucidate the mechanism accounting for the damping of ZFM from the perspectives of mass and energy transport

COMPUTATIONAL METHODS

CONSISTENCY OF HYDRODYNAMICS AND THE FLUCTUATION-DISSIPATION THEOREM

DSF AT TWO-TEMPERATURE STATES

HYDRODYNAMIC INSIGHTS INTO THE ATOMIC SCALE

SUMMARY