Metals that are not such
Treating insulators as metals is sometimes needed (e.g., magnetic insulators). There is a minor aesthetic problem with the resulting position of the Fermi energy: it should ideally be in the middle of the gap, but in practice it can be found anywhere, sometimes close to the HOMO or to the LUMO. Under some rather peculiar circumstances, however, the problem is not purely aesthetic; the "m-v" and "m-p" smearing may produce an incorrect Fermi energy, close to the HOMO, because occupancies are not strictly bound between 0 and 1 and there can be two solutions with the correct global occupancy. One possible solution (suggested by SdG) is to use gaussian smearing (that does not suffer from such problem) to find a first value for Ef, then use 'm-v' or 'm-p' bracketing between Ef+sigma and Ef-sigma (or 2 sigma o sigma/2).