ELECTRONIC-STRUCTURE AND CRYSTALLINE ELECTRIC-FIELD IN RCO5 (R=Y, LA,CE, PR, ND, SM, GD, AND TB)

Self consistent charge and spin-polarized local spin density approxima tion functional theory calculations based on the discrete variational method have been performed for RCo5 (R = Y, La, Ce, Pr, Nd, Sm, Gd, an d Tb) compounds. The partial density of states of the Pr atom in the P rCo6Co12 cluster is established to be strikingly similar to that of th e Ce atom in the CeCo6Co12 cluster, supporting the suggestion that the Pr atom is valence fluctuating. The radii <r(4f)> and <r(4f2)> of the 4f electrons of the R atom from La to Tb, except Ce, show the lanthan ide contraction. The crystalline electric field (CEF) parameter A(2)(0 ) at the R site is calculated using a real charge distribution rho(R) in the cluster, except for Pr and Nd, and is in agreement with that ev aluated based on the single-ion model. This result shows that the CEF parameter A(2)(0) is mainly determined by the near electronic structur e. There exists a hybridization in a certain degree between the light rare-earth R-4f and Co-3d orbitaIs in some single-electron-molecular-o rbitals, which are near the Fermi energy level and occupied by electro ns. For light rare-earths the R-4f electrons in RCo6Co12(R = Y, La, Ce , Pr, Nd, and Sm) clusters are not localized entirely and a small amou nt of the R-4f electrons have itinerant properties.