Structural and dynamic features of liquid Si under high pressure above the melting line minimum

TL;DR

This study uses ab initio simulations to analyze how the structure and dynamics of liquid silicon change under high pressure above its melting line minimum, revealing pressure-dependent structural ordering and collective mode behaviors.

Contribution

It provides new insights into the pressure-induced structural and dynamic features of liquid silicon above the melting line minimum, including the evolution of collective excitations and transverse modes.

Findings

Tetrahedral ordering decreases with pressure.

Diffusion coefficient decreases linearly with atomic volume.

Two-peak structure in velocity autocorrelation spectra at high pressures.

Abstract

We report an {\it ab initio} simulation study of changes in structural and dynamic properties of liquid Si at 7 pressures ranging from 10.2 GPa to 24.3 GPa along the isothermal line 1150~K, which is above the minimum of the melting line. The increase of pressure from 10.2 GPa to 16 GPa causes strong reduction in the tetrahedral ordering of the most close neighbors. The diffusion coefficient shows a linear decay vs drop in atomic volume, that agrees with theoretical prediction for simple liquid metals, thus not showing any feature at the pressures corresponding to the different crystal phase boundaries. The Fourier-spectra of velocity autocorrelation function shows two-peak structure at pressures 20 GPa and higher. These characteristic frequencies correspond well to the peak frequencies of the transverse current spectral function in the second pseudo-Brillouin zone. Two almost flat branches of short-wavelength transverse modes were observed for all the studied pressures. We discuss the pressure evolution of characteristic frequencies in the longitudinal and transverse branches of collective modes.