Electro-vibrational coupling effects on “intrinsic friction” in transition metal dichalcogenides

Abstract

We propose a protocol to disentangle the electro-vibrational structural coupling contributing to the intrinsic tribologic properties of layered MX₂ transition metal dichalcogenides (M = Mo, W; X = S, Se, Te) under load. We employ ab initio techniques to model how changing the interlayer distance affects the electronic distribution and the vibrational properties of the system. We analyze the electro-vibrational coupling features by combining orbital polarization and mode Grüneisen parameters analyses with the recently developed bond covalency descriptor and the lattice dynamic metric named cophonicity. We find that intralayer charge distribution depends on the interlayer distance, determining, in turn, a shift of specific vibrational frequencies. We finally suggest a route to control the frequency shift, thus the bulk response to the load, in transition metal dichalcogenides through a proper selection of the atomic type.