Studies of the phonon density of states in ab initio generated amorphous structures of pure silicon

Using a 216-atom amorphous periodic cubic supercell generated with the ab initio ‘undermelt-quench’ procedure previously reported, we have undertaken the study of vibrational properties of pure amorphous silicon, a-Si, with a density of 2.33 g/cm3. The radial distribution function obtained for the 216-atom random structure agrees with previous results for a 64-atom structure. For the density functional calculation the Harris-relaxed structure was used to obtain the vibrational modes. For the classical calculation the structure, obtained with the Harris functional, was relaxed using the Tersoff potential and the vibrational modes calculated. Both results agree very well with experiment indicating that our amorphous cell closely resembles the real material.