Universality in the Vibrational Spectra of Amorphous Systems

Abstract

We have studied both clusters and bulk systems while investigating amorphous states. We have varied the nature of interaction amongst the particles of the system under consideration in order to reveal the possible presence of universality (i.e. independence of the potential). For clusters, the number of particles is varied to investigate the effect of finite size on various properties. To study bulk amorphous systems, we actually use periodic crystals with as large a primitive cell as possible. For any finite disorder, the number of particles in the primitive cell should ideally be made arbitrarily large. However, in practice, this is limited by the available computational resources. We should note here that due to the periodic nature of our approximation to the bulk disordered system, the analysis of spectral fluctuations becomes a lot more subtle and has not been reported in this thesis. We report results only on: (1) Universality in the density of states for clusters, (2) Universality in spectral fluctuations in the case of clusters, and (3) Universality in the density of states for bulk amorphous systems.