Both dscf and ridft require the control file and starting orbitals obtained from the extended Hückel guess using define.
Energy calculations using dscf can be performed in a direct or semi-direct mode. In the direct mode all four-center ERI’s are recalculated at each SCF iteration. The semi-direct mode uses a selective storage of the most time consuming and frequently used integrals. The amount of integrals stored is controlled by the keywords $thize and $thime, related to integral size and computational cost. The semi-direct mode requires a separate dscf statistics run to estimate the disk space needed for integral storage. The statistics run requires the keyword $statistics dscf to be present in the control file. It can be set either manually or using the tool Stati.
For ridft and rdgrad following additional prerequisites are required: