Calculation of Grüneisen Constants in Si

Lattice dynamical calculations of the Grüneisen constants for general strain components are performed using the bond charge model of Weber with additional assumptions on anharmonic forces. The model is adjusted to fit data available at the Γ, X, and L points from various experimental techniques. The results along the main symmetry axes indicate that the Grüneisen constants depend sensitively on those model parameters which were originally determined from the phonon dispersion in the harmonic approximation. It is concluded that for a consistent description of phonon dispersion and anharmonic properties the model has to be revised.