First principles calculations of elastic properties under pressure in SiC

First principles density functional theory is employed to study the elastic constants and sound velocities in wurtzite-SiC under pressure. The focus is on the behavior of the elastic constants (Cij  ) and sound velocities (Cij/ρ) as a function of pressure. The pressure dependences of the transverse acoustic modes in sound velocities which correspond to the wurtzite to rocksalt phase transformation is analyzed. We found that the phase transformation from wurtzite to rocksalt structure relates to an orthorhombic strain with two components: (1) a traceless compression along the [0 0 0 1] axis which corresponds to the sound velocity C44/ρ and (2) a traceless compression along [011¯0] direction which corresponds to the sound velocity C66/ρ.