Atomistic simulation of Si-Ge clathrate alloys

The structural, elastic, vibrational and thermodynamic properties of Si-Ge clathrate alloys have been investigated by lattice dynamics (LD) and molecular dynamics (MD) calculations based on the Tersoff's potential. The structural properties, static cohesive energies and bulk moduli determined from the LD simulations agree with the results of the first-principles approach in the literature. In addition, we estimated the Debye temperatures from the calculated elastic constants. They demonstrate a decay trend as the Ge composition increases. The vibrational properties, especially the phonon density of states, were investigated in comparison with those of the ordinary Si-Ge diamond-like alloys. The MD calculations were then carried out for the clathrate alloys above their respective Debye temperatures to obtain the pair correlation functions and the internal energies.