Ab initio molecular dynamics study of collective dynamics in liquid Tl: Thermo-viscoelastic analysis

¹ Institute for Condensed Matter Physics, NAS of Ukraine, Svientsitskii Street 1, 79011 Lviv, Ukraine
² Institute for Applied Mathematics and Fundamental Sciences, Lviv Polytechnic National University, S. Bandera Str. 12, 79013 Lviv, Ukraine

^* e-mail: bryk@icmp.lviv.ua
^** e-mail: demchuk@icmp.lviv.ua

Published online: 21 August 2017

Abstract

We studied collective dynamics of pure liquid metal Tl using a combination of ab initio molecular dynamics (AIMD) simulations and a thermoviscoelastic model applied to calculations of dynamic eigenmodes and dispersion of collective excitations in particular. We found that for liquid Tl at ambient pressure the transverse current spectral functions obtained directly in ab initio simulations for wave numbers larger than first pseudo-Brillouin-zone boundary contain two low-and high-frequency peaks that is an evidence of emergence of the unusually high-frequency transverse modes as it was observed before in liquid Li at very high pressures. The thermo-viscoelastic dynamic model shows perfect reproduction of the simulation-derived longitudinal current autocorrelation functions, and the acoustic eigenmodes are in nice agreement with the peaks of the longitudinal current spectral functions up to the first pseudo-Brillouin-zone boundary. The deviation of the dynamic eigenmodes from peak positions at higher wave numbers gives evidence of L-T coupling effects.