Origin of the anomalous absence of hydride formation by ZrPd2.

Intermetallic compounds based on hydrogen absorbing elements usually form stable hydrides. This is the case for PdZr2. Surprisingly, ZrPd2 does not absorb hydrogen although both compounds have the same crystal structure and satisfy the empirical geometrical criteria for hydride formation. Results of ab initio calculations reveal an unanticipated purely electronic origin. These results have implications in the search for new intermetallics for hydrogen storage.