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.