Approximate ab initio calculations were made of the vibrational properties of hydrogenated amorphous material by using molecular dynamics methods. A 216-atom model for pure amorphous material was used as a starting point; with voids that were made by removing a cluster of atoms from the bulk and terminating the resultant dangling bonds with H atoms. The calculations showed that the presence of voids led to localized low-energy (30 to 50/cm) states in the vibrational spectrum of the system.

Approximate ab initio calculation of vibrational properties of hydrogenated amorphous silicon with inner voids S.M.Nakhmanson, D.A.Drabold: Physical Review B, 1998, 58[23], 15325-8