In DFT, why do most texts ignore/don't mention the attractive exchange "force" between two antiparallel spins electrons?
The repulsive "exchange" force of two same spins electrons are always mentioned to correct the Coulombic repulsion, which is logical. But books and youtube lectures often ignore the fact that there is an exchange "force" between two antiparallel spins that are attractive. And given that electrons are fermions, with antisymmetric spin wavefunction and symmetric space wavefunction, shouldn't we be emphasizing more on this force?
- Is the correlation energy the Coulombic interaction that was ignored when we were considering the indistinguishability of the two electrons? If so, it should be present in both same spin electrons and different spin electrons, right? In the context of DFT, it seems that we always consider the correlation repulsion of different spin electrons.