Crystal structure prediction of LiBeH3 using ab initio total-energy calculations and evolutionary simulations

The stable crystal structure of LiBeH3 is predicted on the basis of ab initio total-energy calculations using density-functional theory and an extended database of candidate structures and using global optimizations based on an evolutionary algorithm. At the level of density-functional theory, a CaSiO3_1-type structure with space group P2(1)/c, containing BeH4 tetrahedra linked in chains, is the ground-state structure of LiBeH3 (alpha-LiBeH3). It is found to be lower in energy than the structures proposed in previous studies. The analysis of the electronic structure shows that alpha-LiBeH3 is an insulator with a band gap of about 4.84 eV and exhibits strong covalent bonding in the BeH4 tetrahedral complexes. Calculations at finite temperatures and high pressures suggest that at T=408 K and ambient pressure a structural transition from alpha-LiBeH3 (CaSiO3-type) to a YBO3-type structure with space group Cmcm occurs and that at a pressure of 7.1 GPa alpha-LiBeH3 undergoes a pressure-induced structural transition from the alpha-phase to a MgSiO3-type structure with space group C2/c. The calculated enthalpies of formation (-45.36 and -30.12 kJ/mol H-2 without and with zero-point energy corrections) are in good agreement with the experimental result, indicating that LiBeH3 is a potential hydrogen storage material with low activation barriers for hydrogen desorption.