It is often the case that a single algorithm is not able to guarantee SCF convergence. Meanwhile, some SCF algorithms (e.g., ADIIS) can accelerate convergence at the beginning of an SCF calculation but becomes less efficient near the convergence. While a few hybrid algorithms (DIIS_GDM, RCA_DIIS) have been enabled in Q-Chem’s original SCF implementation, in GEN_SCFMAN, we seek for a more flexible setup for the use of multiple SCF algorithms so that users can have a more precise control on the SCF procedure. With the current implementation, at most four distinct algorithms (usually more than enough) can be employed in one single SCF calculation based on GEN_SCFMAN, and the basic job control is as follows:
Note: $rem variables GEN_SCFMAN_ALGO_X, GEN_SCFMAN_ITER_X, GEN_SCFMAN_CONV_X (X = 2, 3, 4) are defined and used in a similar way.
$molecule 2 1 Cd 0.000000 0.000000 0.000000 N 0.000000 0.000000 -2.260001 N -0.685444 0.000000 -4.348035 C 0.676053 0.000000 -4.385069 C 1.085240 0.000000 -3.091231 C -1.044752 0.000000 -3.060220 H 1.231530 0.000000 -5.300759 H 2.088641 0.000000 -2.711077 H -2.068750 0.000000 -2.726515 H -1.313170 0.000000 -5.174718 $end $rem JOBTYPE SP EXCHANGE B3LYP BASIS 3-21g UNRESTRICTED FALSE SYMMETRY FALSE SYM_IGNORE TRUE THRESH 14 SCF_GUESS CORE GEN_SCFMAN_HYBRID_ALGO TRUE GEN_SCFMAN_ALGO_1 ADIIS GEN_SCFMAN_CONV_1 3 !switch to DIIS when error < 1E-3 GEN_SCFMAN_ITER_1 50 GEN_SCFMAN_ALGO_2 DIIS GEN_SCFMAN_CONV_2 8 GEN_SCFMAN_ITER_2 50 $end