Empirical potential description of energetics and thermodynamic propertiesin expanded-volume silicon clathrates - art. no. 195409

Energetics and thermodynamic properties of some expanded-volume silicons ha ve been investigated using an empirical bond-order potential developed by T ersoff. For the most important silicon clathrate networks Si-34 and Si-46, we report on their elastic properties, vibrational properties, thermodynami c proper-ties (free energy, entropy, heat capacity, and melting temperature ), and the formation energies of vacancy, using the harmonic approximation and/or molecular-dynamics simulations. In order to illustrate relations bet ween energetics and geometrical properties in expanded-volume silicons, we have calculated optimized geometries and energetics for more than 60 kinds of silisils, "zeolite without oxygen," introduced by the Arizona State Univ ersity group. A simple relation between cohesive energies and geometrical p roperties is found in these systems. It is also found that bulk moduli in t hese structures strongly depend on the density (or the atomic volume) and a simple theory deduced from the pseudopotential total-energy formalism by L am et al. [Phys. Rev. B 35, 9190 (1987)] holds in the relation between them .