Voronoi-Delaunay analysis of normal modes in a simple model glass

TL;DR

This paper integrates harmonic vibrational analysis with Voronoi-Delaunay geometric analysis in a model glass, revealing correlations between local structure and vibrational modes, and identifying distinct mode subgroups.

Contribution

It introduces a novel approach combining structural geometry with vibrational analysis to study atomic motions in a model glass.

Findings

Structure potentials vary little with frequency except at extremes.

Atoms transition between local structures during soft modes.

A structure-based dynamical matrix indicates a boson peak.

Abstract

We combine a conventional harmonic analysis of vibrations in a one-atomic model glass of soft spheres with a Voronoi-Delaunay geometrical analysis of the structure. ``Structure potentials'' (tetragonality, sphericity or perfectness) are introduced to describe the shape of the local atomic configurations (Delaunay simplices) as function of the atomic coordinates. Apart from the highest and lowest frequencies the amplitude weighted ``structure potential'' varies only little with frequency. The movement of atoms in soft modes causes transitions between different ``perfect'' realizations of local structure. As for the potential energy a dynamic matrix can be defined for the ``structure potential''. Its expectation value with respect to the vibrational modes increases nearly linearly with frequency and shows a clear indication of the boson peak. The structure eigenvectors of this dynamical matrix are strongly correlated to the vibrational ones. Four subgroups of modes can be distinguished.