4.5.2 Basic Convergence Control Options

MAX_SCF_CYCLES
       Controls the maximum number of SCF iterations permitted.
TYPE:
       INTEGER
DEFAULT:
       50
OPTIONS:
       $n$ $n>0$ User-selected.
RECOMMENDATION:
       Increase for slowly converging systems such as those containing transition metals.

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 $\mathrm{𝐇𝐝}=-𝐠$ 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 and 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 small HOMO-LUMO gaps and DIIS fails to converge, LS_DIIS could help. Use ROBUST or ROBUST_STABLE (see 4.5.13) if nothing works; please report failed SCF convergence to the Q-Chem Office to help refine these workflows.

SCF_CONVERGENCE
       SCF is considered converged when the wave function error is less that ${10}^{-\mathrm{SCF}\mathrm{\_}\mathrm{CONVERGENCE}}$. Adjust the value of THRESH at the same time. Note as of Q-Chem 3.0 the DIIS error is measured by the maximum error rather than the RMS error.
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:
       $n$ Corresponding to ${10}^{-n}$
RECOMMENDATION:
       Tighter criteria for geometry optimization and vibration analysis. Larger values provide more significant figures, at greater computational cost.