Kondo--lattice-like effects of hydrogen in transition metals

TL;DR

This paper explores a Kondo-like effect of hydrogen in transition metals, showing how strong orbital breathing leads to local singlet states and impacts the material's electronic properties, explaining discrepancies in theoretical predictions.

Contribution

It introduces a model where hydrogen's orbital breathing causes occupation-dependent hopping, revealing a new mechanism for local singlet formation in transition metals.

Findings

Orbital breathing causes strong occupation-dependent hopping.

Formation of local singlet-like bound states involving hydrogen.

LDA fails to account for these effects, leading to incorrect metallic predictions.

Abstract

We discuss the possibility of a Kondo like effect associated with H in metals resulting from the strong dependence of the H1s 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 singlet-like 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 LDA to incorporate this correction is probably responsible for the incorrect prediction of a metallic ground state for the YH3 switchable mirror compounds.