Vibron-vibron coupling from ab initio molecular dynamics simulations of a silicon cluster

TL;DR

This study investigates temperature effects on vibrational modes of a silicon cluster and introduces an ab initio computational method to quantify vibron-vibron coupling strengths, revealing moderate temperature-dependent increases.

Contribution

The paper presents a novel ab initio approach to extract vibron-vibron coupling strengths in clusters or molecules from molecular dynamics simulations.

Findings

Blue shift of Si-Si vibrational modes with temperature

Red shift of other vibrational modes with temperature

Vibron-vibron coupling strength up to 2.5 THz, increasing slightly with temperature

Abstract

We study the temperature dependent dynamical processes of a Si10H16 cluster and obtain a blue shift of the Si-Si vibrational modes with transverse acoustic character and a red shift of the other vibrational modes with increasing temperature. We link this behavior to the bond length expansion and the varying sign of the Grueneisen parameter. We further present a computational approach able to extract the vibron-vibron coupling strength in clusters or molecules. Our approach is based on ab initio Born-Oppenheimer molecular dynamics and a projection formalism able to deliver the individual vibron occupation numbers. From the Fourier transform of the vibron energy autocorrelation function we obtain the coupling strength of each vibron to the most strongly coupled vibronic states. We find vibron-vibron coupling strength up to 2.5 THz with a moderate increase of about 5 % when increasing the temperature from 50 to 150 K.