Pht. Philipsen et Ej. Baerends, COHESIVE ENERGY OF 3D TRANSITION-METALS - DENSITY-FUNCTIONAL THEORY ATOMIC AND BULK CALCULATIONS, Physical review. B, Condensed matter, 54(8), 1996, pp. 5326-5333
We report generalized gradient approximation (GGA) cohesive energies f
or 3d metals. The problem of obtaining atomic reference energies in de
nsity-functional theory is considered. The effect of going to nonspher
ical atomic charge distributions is much larger at the GGA than at the
local-density approximation (LDA) level, but allowing fractional occu
pations of 3d and 4s shells has negligible effect. When nonsphericity
effects are taken into account in the atomic reference energies, the a
verage absolute error of 0.3 eV in the GGA cohesive energies is much s
maller than the LDA error of 1.3 eV. The working of the GGA is analyze
d in terms of the cohesive energy density and the charge inhomogeneity
division of the exchange energy. The low-gradient limit in the GGA fu
nctionals is not important as regions with charge inhomogeneity s<0.2
have negligible contributions.