THERMODYNAMIC PROPERTIES OF C-SI DERIVED BY QUANTUM PATH-INTEGRAL MONTE-CARLO SIMULATIONS

Feynman path-integral Monte Carlo simulations of crystalline silicon, using the empirical potential of Stillinger and Weber, have been perfo rmed in the isothermal-isobaric ensemble. Several thermodynamic proper ties have been evaluated as a function of pressure and temperature. Th e calculated lattice parameter, heat capacity, thermal expansion coeff icient, and bulk modulus show an overall agreement with the experiment al data. However, the negative thermal expansion of silicon at tempera tures below 120 K is not reproduced with this model potential. The imp ortance of anharmonicity and quantum effects on the properties derived from the Stillinger-Weber potential is addressed by comparison with t he results expected in a quasiharmonic approximation and in the classi cal limit.