At the microscopic level, what determines whether a given set of valence elections has an excess spin, and thus an excess magnetic moment, is still determined b

At the microscopic level, what determines whether a given set of valence elections has an excess spin, and thus an excess magnetic moment, is still determined by an empirical set of rules, called Hund's rules, instead of from first principles, iirc: https://en.wikipedia.org/wiki/Hund%27s_rules https://en.wikipedia.org/wiki/Hund%27s_rules