The entry number_bands gives the number of bands that are computed. It should always be slightly more than the minimum number of bands required, unless a wide-gap insulator is studied. If the number is more than the minimum, the Grassmann_metal diagonalization is suggested. For systems with a large number of states at the Fermi surface (such as metallic surfaces), as many as twice the minimum number of bands is optimum. The computational effort grows linearly with the number of bands, so do not pick the number unreasonably large either.
Example:
number_bands 12
Default: There is no default