spin-dependent band gap calculations

Sebas_Na_Osle

Dear colleagues,
I am trying to deal with quantum-chemical calculations of metal-containing coordination polymers, and I have a question which turned out to be difficult to me:

If a system includes copper atoms, which implies that it has 'unpaired' electron, how to describe a band gap in this case? I mean we can estimate two different band gaps for 'spin-up' and 'spin-down' channels, but what should we take as a reference to compare with experimental data?

If you can advise me some literature on this, it would be also great.

Thank you