Electronic structure of metal hydrides. II. Band theory of Sc<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>and Y<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Abstract

Self-consistent band-structure calculations have been performed for Sc${\mathrm{H}}_{2}$ and Y${\mathrm{H}}_{2}$ using the Korringa-Kohn-Rostoker method. The results indicate a net charge transfer from the metal to the hydrogen site and a concomitant raising of the hydrogen bonding bands relative to those obtained through non-self-conssitent calculations. Comparisons are made between the results of our calculations and the results of optical studies by Weaver, Rosei, and Peterson. Additional calculations were performed in which the Fermi level or band gaps were rigidly shifted by a small energy increment. These calculations were used to simulate the derivative structure obtained in thermomodulation spectra and helped to identify the $k$-space origin of several experimental interband features found in the thermoreflectance of Sc${\mathrm{H}}_{2}$ and Y${\mathrm{H}}_{2}$. The experimentally observed, low-energy, stoichiometry-dependent optical features of Y${\mathrm{H}}_{2}$, which had partially inspired our studies, were not interpretable within the framework of our calculations based on the Ca${\mathrm{F}}_{2}$ structure in which the hydrogen occupies all of the available tetrahedral sites. Instead, indirect evidence suggests that these low-energy features are associated with partial occupation of octahedral sites.