The effect of relaxation on the structural and electronic properties of a terbium superstoichiometric dihydride

The electronic structure and equilibrium properties for the cubic rare earth superstoichiometric dihydride TbH2.25 are calculated using the full-potential linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT) in the generalized gradient approximation (GGA) and local density approximation (LDA) as implemented in the WIEN2k simulation code at 0 K. The structure of TbH2.25 is stabilized by local atomic relaxations in both approximations. The atomic positions under relaxation calculated with the GGA are closer to the ideal atomic positions than those calculated with the LDA. The GGA calculated equilibrium lattice constant is in excellent agreement with the available experimental data. The calculation of the density of states, electronic charge density and energy band structures show that this superstoichiometric dihydride has a metallic character with a mixed covalent and ionic bonding.