First-principles calculations of elastic and electronic properties of NbB2 under pressure

The structural parameters, elastic constants and electronic structure of NbB2 under pressure are investigated by using first-principles plane-wave pseudopotential density functional theory within the generalized gradient approximation (GGA). The obtained results are in agreement with the available theoretical data. It is found that the elastic constants and the Debye temperature of NbB2 increase monotonically and the anisotropies weaken with pressure. The band structure and density of states (DOS) of NbB2 under pressure are also presented. It is the sigma hole that determines the superconductivity in NbB2, and the features of the sigma bands are unchanged after applying pressure except for a shift of position. The density of states (DOS) at the Fermi level decreases with increasing pressure, in conjunction with Bardeen Cooper-Schrieffer (BCS) theory, which can predict T-c decreasing with pressure, in agreement with the trend of the theoretical T-c versus pressure