Drastic changes of electronic structure, bonding properties and crystal symmetry in Zr sub(2)Cu by hydrogenation, from ab initio

Gradual hydrogen uptake into Zr sub(2)Cu intermetallic leads to crystal symmetry changes from tetragonal Zr sub(2)CuH sub(2) to monoclinic Zr sub(2)CuH sub(5). This experimental finding is explained here from cohesive energies computed within quantum DFT for Zr sub(2)CuH sub(x) (x = 1, 2, 3, 4, 5) models in both structures. The threshold is found at 2 < x < 3 in agreement with experiment. Beside structural crossover, electronic properties, chemical bonding, and mechanical behavior are also analyzed. Metal-H interactions arising from increasingly H presence in Zr sub(2)Cu lead to more and most cohesive and harder Zr sub(2)CuH sub(2) and Zr sub(2)CuH sub(5) respectively.