I’m reading Assa Auerbach’s Interacting electrons and quantum magnetism.
In 1.3, it says
In contrast, transition metals and mixed valence rare earth compounds contribute $d$ and $f$ electrons to the conduction band. There, the electrons are mostly localized within a small radius $\langle r_{ij}\rangle \ll a$ around the ions, where $a$ is the lattice spacing.
I wonder why are $d$ and $f$ electrons near to the ions?