Band structure, cohesive properties, and Compton profile ofγ- andα-cerium

Abstract

Recent Compton scattering experiments on the high-volume ($\ensuremath{\gamma}$) and low-volume ($\ensuremath{\alpha}$) phases of fcc cerium and their interpretation in terms of the renormalized-free-atom model cast severe doubts on the model of Pauling and Zachariasen for the $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\alpha}$ transition. Stimulated by these results, we have extended a previous self-consistent local-density band-structure investigation to study the Compton profiles of $\ensuremath{\gamma}$- and $\ensuremath{\alpha}$-cerium. For the band structure, Bloch functions, and their Fourier transforms we use the linear muffin-tin orbital method in the atomic-sphere approximation. We analyze the calculated Compton profiles in terms of band structure and local angular momentum character of the wave functions. The change in band structure and wave functions under compression (with approximately one electron per atom in the $4f$ band of both phases) accounts well for the observed change in the Compton profile. This provides further evidence against the model in agreement with the analysis of Kornst\adt et al. In addition, we study the cohesive energy of fcc cerium as a function of volume in the local-density approximation. For $\ensuremath{\alpha}$-cerium in the ${4f}^{1}{(5d6s)}^{3}$ configuration we find a cohesive energy of 5.4 eV/atom in good agreement with experiment, whereas the promotional ${4f}^{0}{(5d6s)}^{4}$ state yields a binding energy of 0.6 eV/atom only. Therefore the fourth valence electron has to be a $4f$ electron, and $\ensuremath{\alpha}$-cerium has to be regarded as an $f$-band metal.