Density functional methods for the magnetism of transition metals: SCAN in relation to other functionals

We report tests of various density functionals for ferromagnetic Fe, Co, and Ni with a focus on characterizing the behavior of the so-called strongly constrained and appropriately normed (SCAN) functional. It is found that SCAN is closer in behavior to functionals that yield localized behavior, such as hybrid functionals, than other semilocal functionals that are tested. The results are understood in terms of a tendency to differentiate orbitals, favoring integer occupation, which is necessary for a correct description of atomic systems, but inappropriate for the open shell metallic ferromagnetic metals studied here. Not only is the exchange splitting for open shells enhanced with SCAN, but also as seen in Ni, there is much more band dependence with significantly more overestimation for bands corresponding to the partially filled orbitals.