Failure of the SCAN functional for itinerant magnets and the reasons*

The SCAN functional fails dramatically in its description of itinerant magnets including the elements Fe, Ni and Co. We report 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. This has to do with the fitted nature of SCAN where it reproduces selected “norms”.