Structural, electronic and optical properties of BeH2: A density functional theory study

Based on density functional theory, the structural, electronic and optical properties of alpha-,beta-,gamma-,delta- and epsilon-BeH2 have been investigated using the plane-wave pseudo-potential and Broyden-FletcherGoldfarb- Shanno approaches. The calculated equilibrium structural parameters are in excellent agreement with the experimental and other theoretical results. The mechanical stabilities of BeH2 were determined by phonon spectrum calculation, indicating that alpha-,gamma-,delta- and epsilon-BeH2 are dynamically stable, but beta-BeH2 is dynamically unstable. The band structures and density of states of BeH2 were calculated and analyzed in detail. Four common characteristics of the valence bands and conduction bands for BeH2 were described. The alpha-and beta-BeH2 exhibit direct band gap characteristics, and the gamma-, delta-and epsilon-BeH2 are indirect band gaps. Mulliken population analysis of BeH2 indicates that the charge populations of H1s and Be 2p states are very obvious, but Be 2s states are relatively weak; the charge transfers are from Be-H, and all of the BeH2 are mixture bonding materials (covalent + ionic bond) and the covalent character is obvious. By combining the electronic properties and frequencydependent dielectric function epsilon(omega), the linear response optical properties of BeH2 were predicted with a photoelectron energy up to 30 eV.