Path-integral Monte Carlo study of amorphous silicon

Amorphous silicon (a-Si) is studied by path-integral Monte Carlo simulations. These quantum atomistic simulations allow one to analyze the temperature dependence of the kinetic and potential contributions to the vibrational energy of the material, as well as the atomic mean-square displacements, further than the harmonic approximation. The results obtained for a-Si are compared with those found in similar quantum simulations of crystalline silicon (c-Si). The anharmonicity of the atom vibrations in a-Si is larger than in its crystalline counterpart, as seen by the kinetic-to-potential energy ratio (virial theorem) and by comparison to a harmonic approach for the solid vibrations. The amplitude of the atomic motion in a-Si is found to be larger than in c-Si, as a consequence of the presence of low-energy vibrational modes in the amorphous material. This amplitude is enhanced further by anharmonicities in the interatomic potential.