Model calculations for the vibrational anomalies of a disordered Lennard-Jones solid

Using a modified version of the two-site coherent potential approximation (CPA), also known as effective medium approximation (EMA), we can calculate the density of states (DOS) of a disordered rare-gas-solid modelled by a Lennard-Jones potential. As input we use the radial pair distribution of a pertinent molecular-dynamics simulation of Rahman et al. The resulting DOS agrees well with that of the simulation. The DOS exhibits an anomalous enhanced low-frequency contribution (boson peak''). We investigate and discuss the influence of the quenched structure on this anomaly and on the resulting sound velocity. (C) 2000 Published by Elsevier Science B.V. All rights reserved.