Kondo-lattice–like effects of hydrogen in transition metals

We discuss the possibility of a Kondo-like effect associated with H in metals, resulting from the strong dependence of the H $1s$ orbital radius on the occupation number. We demonstrate that such a strong breathing property of the orbital radius, which translates directly into a strong occupation-dependent hopping, results in the formation of local singletlike bound states involving one electron on H and one on the surrounding metal orbitals. We also show that already at a mean-field level an occupation-dependent hopping integral leads to a substantial potential-energy correction on hydrogen, and that the failure of band-structure methods to incorporate this correction is responsible for the incorrect prediction of a metallic ground state for the ${\mathrm{YH}}_3$ switchable mirror compounds.