4.5 Converging SCF Calculations

4.5.8 Direct Minimization (DM)

(May 16, 2021)

Direct minimization (DM) is a less sophisticated forerunner of the geometric direct minimization (GDM) method discussed in the previous section. DM does not properly step along great circles in the hyper-spherical space of orbital rotations, and therefore converges less rapidly and less robustly than GDM, in general. DM is retained in Q-Chem only for legacy purposes. In general, the input options are the same as for GDM, with the exception of the specification of SCF_ALGORITHM, which can be either DIIS_DM (recommended) or DM.

       When SCF_ALGORITHM = DM, this controls the way the initial step, and steps after subspace resets are taken.
       FALSE Use Roothaan steps when (re)initializing TRUE Use a steepest descent step when (re)initializing
       The default is usually more efficient, but choosing TRUE sometimes avoids problems with orbital reordering.