Ab-initio study of structural phase transitions and optoelectronic properties in BeH2 at increasing pressure

• α-BeH2 (insulator) ⟹29.40GPa β-BeH2 (metallic) ⟹53.77GPa γ-BeH2 (semiconducting).
• In BeH2 obtaining high-pressure phases with superconducting properties is possible.
• Equilibrium volume collapse from α- to β-phase»β- to γ-phase transition.
• Obtained dielectric constant for α-BeH2 is in excellent agreement with earlier reported value.
• BeH2 shows anisotropic behavior in all three studied phases.

The structural stability, electronic and optical properties of BeH2 under high pressure have been studied using the density functional theory (DFT) employing full potential-linearized augmented plane wave (FP-LAPW) method. The exchange correlation functional has been solved using the generalized gradient approximation. The calculations show that BeH2 becomes unstable upon application of pressure. At a pressure of 29.40 GPa the ground state α-BeH2 transforms to hypothetical phase β-BeH2 and further at a pressure of 53.77 GPa (with respect to the ground state α-BeH2) β-BeH2 transforms to γ-BeH2. In α-BeH2 phase it remains as an insulator while in β-BeH2 phase its behavior becomes metallic. But upon further increase in pressure it becomes a semiconductor in γ-BeH2 phase. Hence the possibility of obtaining high-pressure phases with superconducting properties cannot be ruled out. There occurs a huge equilibrium volume collapse at α- to β-phase transition and relatively smaller volume changes at β- to γ-phase transition. Our obtained value of dielectric constant (3.0) for α-BeH2 is in excellent agreement with earlier reported value (3.1). Also BeH2 shows anisotropic behavior in all three studied phases.