Structural, electronic and optical properties of LiBeP in its normal and high pressure phases

摘要

An investigation on the structural stabilities, electronic and optical properties of LiBeP under high pressure was conducted using the all-electron density functional theory within the local density approximation. Our results show that the sequence of the pressure induced phase transition of LiBeP is the Cu_2Sb-type structure (P4mm), the MgSrSi-type structure (Pnma) and the LiGaGe-type structure (P6_3mc). The first transition (P4mm to Pnma) takes place at 2.95 GPa and the second (Pnma to P6_3mc) at 6.65 GPa. In the three phases, the bandgap is indirect and the valence band maximum is at the zone center. With increasing pressure LiBeP in the LiGaGe structure becomes a direct gap semiconductor at 19.75 GPa. The assignments of the structures in the optical spectra and the band structure transitions are discussed. The mean value of the optical dielectric constant for the Cu_2Sb phase is smaller than that for the MgSrSi and the LiGaGe ones. This compound has a positive uniaxial anisotropy in the LiGaGe structure. The absorption coefficient along the z direction, α_(zz), for the MgSrSi structure is higher than that in the other two structures in the visible regime.