See also more detailed options in the following sections, and note that the SCF convergence criterion and the integral threshold must be set in a compatible manner, (this usually means THRESH should be set to at least 3 higher than SCF_CONVERGENCE).
MAX_SCF_CYCLES
MAX_SCF_CYCLES
Controls the maximum number of SCF iterations permitted.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
User-selected.
RECOMMENDATION:
Increase for slowly converging systems such as those containing transition
metals.
SCF_ALGORITHM
SCF_ALGORITHM
Algorithm used for converging the SCF.
TYPE:
STRING
DEFAULT:
DIIS
Pulay DIIS.
OPTIONS:
DIIS
Pulay DIIS.
ROOTHAAN
Roothaan repeated diagonalization
DM
Direct minimizer.
L_BFGS
Limited memory BFGS algorithm with line search
GDM
Geometric Direct Minimization
GDM_LS
Like GDM, but employs a line search in L-BFGS
GDM_QLS
Like GDM_LS, but uses a quadratic line search in L-BFGS
RCA
Relaxed-constraint algorithm
ADIIS
The combination of the ARH energy function and DIIS by Hu and Yang
NEWTON_CG
Solve using conjugated gradients to determine Newton steps
(see also NEWTON_MINRES, which uses the MINRES algorithm
to solve the linear equation)
DIIS_DM
Uses DIIS initially, switching to direct minimizer for later iterations
(See THRESH_DIIS_SWITCH, MAX_DIIS_CYCLES)
DIIS_GDM
Use DIIS and then later switch to geometric direct minimization
(See THRESH_DIIS_SWITCH, MAX_DIIS_CYCLES)
LS_DIIS
Uses level-shifting initially, switching to DIIS for later iterations
(See THRESH_LS_SWITCH, MAX_LS_CYCLES)
RCA_DIIS
Use RCA initially, switching to DIIS for later iterations
(See THRESH_RCA_SWITCH and MAX_RCA_CYCLES)
ADIIS_DIIS
Use ADIIS initially, switching to DIIS for later iterations
(See THRESH_ADIIS_SWITCH and MAX_ADIIS_CYCLES)
ROBUST
New black-box workflow for robust convergence featuring tighter
thresholds and a combination of algorithms (DIIS, ADIIS, and GDM).
ROBUST_STABLE
Does stability analysis on top of the ROBUST procedure.
RECOMMENDATION:
Use DIIS unless performing a restricted open-shell calculation, in which case GDM is recommended.
If DIIS fails to find a reasonable approximate solution in the initial iterations,
RCA_DIIS or ADIIS_DIIS are the recommended fallback options.
If DIIS approaches the correct solution but fails to finally converge, DIIS_GDM
is the recommended fallback. For systems with a small HOMO/LUMO gap, and where, DIIS fails to converge,
LS_DIIS may help. If nothing works, try ROBUST or ROBUST_STABLE.
Please report failed SCF convergence to the Q-Chem office, in order to help refine these workflows.
Note: For usage of the ROBUST or ROBUST_STABLE algorithms, see Section 4.5.13. For the Squared Gradient Minimization (SGM) and related algorithms, see Section 4.5.15.
SCF_CONVERGENCE
SCF_CONVERGENCE
SCF is considered converged when the wave function error is
. Adjust the value of THRESH at the same time.
TYPE:
INTEGER
DEFAULT:
5
For single point energy calculations (including BSSE and XSAPT jobs)
7
For job types NMR, STATPOLAR, DYNPOLAR, HYPERPOLAR, and ISSC
8
For most other job types, including geometry optimization, transition-state search,
vibrational analysis, CIS/TDDFT calculations, correlated wavefunction methods,
energy decomposition analysis (EDA2), etc.
OPTIONS:
Corresponding to
RECOMMENDATION:
Tighter criteria for geometry optimization and vibration analysis. Larger
values provide more significant figures, at greater computational cost.
In some cases besides the total SCF energy, one needs its separate energy components, like kinetic energy, exchange energy, correlation energy, etc. The values of these components are printed at each SCF cycle if one specifies SCF_PRINT = 1 in the input.