Vibrational properties of amorphous silicon in the frequency range 250–450cm−1

The phonon densities of states of five- and six-membered rings found in a periodic model of amorphous silicon have been calculated with use of the cluster-Bethe-lattice method with the Born potential. The results are consistent with earlier periodic model calculations, despite the difference in potentials. There is strong evidence that the ring structure is not important in determining the vibrational properties of amorphous silicon. Another cluster which demonstrates the splitting off from the bending and stretching modes in the frequency range 250–450 ${\mathrm{cm}}^{\mathrm{-}1}$ is also investigated. It is shown that the modes for this range are a mixture of this bond bending and bond stretching. In addition, some simplifying properties for cluster-Bethe-lattice calculations are derived.