Cohesive and electronic properties of transition metals: The generalized gradient approximation

We present a comparison between the local-spin-density approximation and the generalized gradient approximation for the calculation of cohesive and electronic properties of transition metals. Atomic s-d promotion energies, equilibrium lattice constants, bulk moduli, magnetic moments, and cohesive energies have been determined for 3d, 4d, and 5d transition metals. Gradient corrections to the density functional seem to have very small effects on calculated atomic s-d promotion energies. In agreement with previous results, we find that the generalized gradient approximation yields equilibrium lattice parameters and bulk moduli that are very close to experimental values for the 3d transition metals, while the results in the 4d and 5d series are less accurate. Cohesive energies calculated with the local-spin-density approximation are found to be too high for all transition metals. The generalized gradient approximation lowers these values, which, however, leads to cohesive energies that are too low in many cases. We argue that a major part of the remaining discrepancy may be due to the muffin-tin-potential approximation.