It seems most of functionals underestimate band gaps for semiconductor materials. I am wondering what is the best functional to use in DMol3 or Castep? B3LYP might be good, but I found DMol3 does not allow band structure calculations with peroidic boundary condition using B3LYP. I am trying PBE0 and HSE06 in CASTEP, and it seems they are extremely slow.  The paper below shows B3PW91 is the best functional, but I can not find either in DMol3 or CASTEP. Is there any way we can import this functional to MS?

DOI: 10.1021/jz101565j  

From DMol3 outmol file, I can get information about the Fermi Energy, Band Gap, lower edge of the Conduction band, and the upper edge of the valance band.  These values are not available directly in the CASTEP output file. Can I get similar information from Castep band structure calculations somehow?

Thank you very much.

Leon