COHESIVE PROPERTIES OF THE LANTHANIDES - EFFECT OF GENERALIZED GRADIENT CORRECTIONS AND CRYSTAL-STRUCTURE

Two different approximations to the density functional, the local (spi n) density approximation (LDA) in the Hedin-Lundqvist parametrization and the Perdew-Wang generalized gradient approximation (GGA), are comp ared using the lanthanide series plus barium as testing ground. Our to tal-energy calculations are parameter-free and all-electron, with a fu ll-potential linear muffin-tin orbital basis set. The equilibrium volu mes, bulk moduli, and generalized cohesive energies are calculated, as suming both the fee and hcp crystal structures, and compared to experi mental data. We find that GGA corrects most of the overbonding tendenc y of LDA for these elements. Our results also suggest that the standar d model of the lanthanides, according to which the 4f shell can be vie wed as chemically inert, is not fully appropriate for the early lantha nides (not including La), and that the trend in the bulk modulus is mu ch less smooth than previously thought.