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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:

GEN_SCFMAN_HYBRID_ALGO

Use multiple algorithms in an SCF calculation based on GEN_SCFMAN.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Use a single SCF algorithm (given by SCF_ALGORITHM).
TRUE
Use multiple SCF algorithms (to be specified).

RECOMMENDATION:

Set it to TRUE when the use of more than one algorithm is desired.

GEN_SCFMAN_ALGO_1

The first algorithm to be used in a hybrid-algorithm calculation.

TYPE:

STRING

DEFAULT:

0

OPTIONS:

All the available SCF_ALGORITHM options, including the GEN_SCFMAN
additions (Section 4.3.1).

RECOMMENDATION:

None

GEN_SCFMAN_ITER_1

Maximum number of iterations given to the first algorithm. If used up, switch
to the next algorithm.

TYPE:

INTEGER

DEFAULT:

50

OPTIONS:

User-defined

RECOMMENDATION:

None

GEN_SCFMAN_CONV_1

The convergence criterion given to the first algorithm. If reached, switch to
the next algorithm.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
10${}^{-n}$

RECOMMENDATION:

None

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