First-principles lattice dynamical study of ScAs and ScSb at zero and high pressure

A first-principles pseudopotential method is used to investigate the structural and elastic properties of ScAs and ScSb in their ambient B1(NaCl) and in high pressure B2 (CsCl) phases and phonon structures at zero and close to phase transition pressure. The calculated lattice constants, static bulk modulus, first order pressure derivative of the bulk modulus and the elastic constants are reported in B1 and B2 structures and compared with available experimental and other theoretical results. The phonon properties of these two compounds are compared among themselves which reveal that these compounds are predominantly metallic, due to degeneracy of optical frequencies at the zone centre. At high pressure, near the B1 to B2 transition, the LA mode at X-point softens leading to structural instability.