From spectroscopic results it has been seen that Half-Metallic compounds may have optical band gap. Band structures of Half-Metals are overlapped by majority (or minority) spin channel. Now how can one relate the electronic band structure to the optical band gap?. Should one go for spin up band gap (or spin down band gap) to explain optical absorption? Seeking some explanations.
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Looking at the bands, in the SrCoWO case you mention you'll have low energy absorption (Drude like), then nothing up to about 2 eV (probably more considering GGA gap errors) and then some gap-like interband absorption. The other cases also show some structure at typical gap-like energies. Using Vasp (e.g.), you can compute the energy-dependent dielectric function in the majority and minority channels separately, and hence the n and k optical constants, and look for structure there. In experiment, any difference between minority and majority will be visible only in some kind of spin resolved spectroscopy (quite likely depending on orientation etc.). In generic absorption measurements you'll see an average of the two dielectric response in the two channels.
related to interband transition in case of band gap. however for metallic system you need to consider intraband transition
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