Effective local environment model for vibrational states in pure amorphous germanium and silicon

A detailed comparison between the measured infrared absorption (IR) spectra of pure amorphous germanium and silicon and the calculated density of vibrational states (DVS) and IR spectra for several models shows the need for an improved model of this system. A small (17 atom) crystalline cluster model is proposed, in which the imbedding of the cluster in the bulk amorphous medium is simulated by nearest-neighbor forces on the surface atoms of the cluster. The surface force constants are adjustable parameters of the model. A DVS is obtained which has the distinct three-peaked form of the measured IR, and systematic variation of the surface parameters show the range in which these may be adjusted to achieve precise agreement with the peak frequencies of the observed IR.