1 6 Ju n 19 99 Voronoi - Delaunay analysis of normal modes in a simple model glass

Voronoi-Delaunay analysis of normal modes in a simple model glass. 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 (Delau-nay 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.