Structural and electronic properties of BeH2 polymorphs: a study by density functional theory

Structural and electronic properties of alpha, beta, delta and epsilon polymorphs of BeH2 are studied. The effect of pressure on these properties is also seen. Investigations are carried out using the linear combination of atomic orbitals method. The lattice parameters, computed by coupling total energy calculations with the Murnaghan equation of state for the four crystals, are overall in agreement with the experimental data and other calculations. Enthalpy-pressure diagram indicates structural phase transitions alpha -> beta, alpha -> delta, alpha -> epsilon, beta -> delta, beta -> epsilon, and delta -> epsilon to occur at 8.75, 12.75, 18.34, 39.53, 55.57 and 76.60 GPa respectively. Electronic band structure and density of states from PBE-GGA show that all polymorphs have wide bandgap. However, quantitative and qualitative agreement of the bandgap from hybrid calculations is observed with available GW data in alpha-BeH2. Therefore bandgaps from hybrid calculations are also proposed. In the three polymorphs the bandgap decreases slowly with pressure. Beyond 100 GPa, the beta structure exhibits overlap of bands at the Gamma point.