Molecular-dynamics investigations of conformational fluctuations and low-energy vibrational excitations in a-Si:H.

First-principles molecular-dynamics simulations on models of a-Si:H and a-Si reveal the existence of a quasicontinuous manifold of nearly degenerate and conformationally distinct metastable minima which are accessible to each other at moderate simulation temperatures in the microcanonical ensemble. Other lowenergy excitations were also observed: elastic modes with anomalously low frequencies, which are somewhat local, though they involve a significant fraction of the atoms constituting supercell models. We investigate these phenomena via molecular dynamics and relate them to previous work on glassy solids and on liquids.