Pressure-dependent properties of SiC polytypes

We present a first-principles study on the pressure-dependent properties of cubic and hexagonal polytypes of silicon carbide (SiC). Our calculations have been performed within density-functional perturbation theory, using the plane-wave pseudopotential approach. The stability of several high-pressure SiC phases is discussed in terms of the ionicity and metallicity of the Si--C bonds. Furthermore, we investigate pressure dependence of the zone-center frequencies, of the Born effective charges, and of the static and high-frequency dielectric constants for 3C, 2H, and 4H polytypes of SiC. Whereas the structural and electronic properties of the cubic and hexagonal polytypes are very similar, remarkable pressure-induced differences are found for the dynamical and dielectric properties. The unusual behavior of the transverse effective charge recently observed experimentally for 6H SiC is discussed. {} 1996 The American Physical Society.