This keyword controls the functioning of the SCF procedure. Options are used to specify the desired behavior, alternate algorithms, and so on. See Efficiency Considerations for more information on maximizing performance in the SCF for difficult problems.
The default SCF procedure uses a combination of EDIIS [Kudin02] and CDIIS, with no damping or Fermi broadening. In Gaussian 09, SCF=Tight is the default.
The SCF=QC option is often helpful with difficult conversion cases. For difficult-to-converge ROHF wavefunctions, where QC cannot be used, add Use=L506 to the route section.
See reference [Schlegel91a] for a discussion of SCF convergence and stability.
ALGORITHM SELECTION OPTIONS
DIIS calls for and NoDIIS prohibits use of Pulay’s Direct Inversion in the Iterative Subspace (DIIS) extrapolation method [Pulay82].
Use only CDIIS. CDIIS implies Damp as well.
Requests temperature broadening during early iterations [Rabuck99], combined with CDIIS and damping. NoFermi suppresses Fermi broadening and is the default. By default, Fermi also implies Damp and also includes level shifting.
Turn on dynamic damping of early SCF iterations. NoDamp is the default. However, damping is enabled if SCF=Fermi or SCF=CDIIS is requested. Note that damping and EDIIS do not work well together.
Allow dynamic damping for up to N SCF iterations (the default is 10).
Calls for the use of a quadratically convergent SCF procedure [Bacskay81]. By default this involves linear searches when far from convergence and Newton-Raphson steps when close (unless the energy goes up). This method is slower than regular SCF with DIIS extrapolation but is more reliable. SCF=QC is not available for restricted open shell (RO) calculations.
Add an extra SCF=QC step in case the first-order SCF has not converged.
Sets the limit on conventional SCF cycles during SCF=XQC to N.
Use pseudo-diagonalization in Link 502 whenever possible, with full diagonalization only at the early cycles, at the end, and every Nth cycle in between. PDiag is a synonym for this option. This is the default for semi-empirical methods (the default is N=30).
Forces full diagonalization in Link 502. This is the default for HF and DFT. FDiag is a synonym for this option.
Does steepest descent SCF
Does scaled steepest descent SCF.
Save k-point information at the conclusion of the SCF. NoSaveKPoint says not to save this data, and it is the default except for numerical frequency calculations for which SaveKPoint is the default.
Calls for use of the direct minimization SCF program [Seeger76]. It is usually inferior to SCF=QC and retained for backwards compatibility and as a last resort. Available only for RHF closed shell and UHF open shell calculations.
Shift orbital energies by N*0.001 (i.e., N milliHartrees); N defaults to 100. This option disables automatic archiving. N=-1 disables level shifting; NoVShift is equivalent to this setting.
Changes the maximum number of SCF cycles permitted to N; the default is 64 (or 512 for SCF=DM and SCF=QC). Note that with DIIS turned on, memory requirements increase with increasing maximum number of cycles.
Specifies that L508 (SCF=QC, SD, or SSD) should do full linear searches at each iteration. By default, a full minimization is done only if the initial microiteration caused the energy to go up.
Set the maximum rotation gradient for a Newton-Raphson step in SCF=QC to 10-N. Above this, scaled steepest descent is used; above 100 times this, steepest descent is used. The default value for N is 2.
FinalIteration performs and NoFinalIteration prevents a final non-extrapolated, non-incremental iteration after an SCF using DIIS or a direct SCF has converged. The default is NoFinalIteration.
Forces use of incremental Fock matrix formation. This is the default for direct SCF. NoIncFock prevents the use of incremental Fock matrix formation, and it is the default for conventional SCF.
For in-core calculations, saves the integrals on disk as well, to avoid recomputing them in Link 1002. Only useful for frequency jobs in conjunction with SCF=InCore. NoPass forces integrals to be recomputed during each in-core phase.
Use tight convergence in linear equation solution throughout SCF=QC. By default, the convergence criterion is tightened up as the rotation gradient is reduced.
Use even tighter convergence in the linear equation solutions (microiterations) throughout the QCSCF. This option is sometimes needed for nearly linearly-dependent cases. VTL is a synonym for VeryTightLinEq.
INTEGRAL STORAGE OPTIONS
Requests a direct SCF calculation, in which the two-electron integrals are recomputed as needed. This is the default SCF procedure in Gaussian. This is possible for all available methods, except for MCSCF second derivatives and anything using complex orbitals.
Insists that the SCF be performed storing the full integral list in memory. This is done automatically in a direct SCF calculation if sufficient memory is available. SCF=InCore is available to force in-core storage or abort the job if not enough is available. NoInCore prohibits the use of the in-core procedure, for both the SCF and CPHF.
The two-electron integrals are stored on disk and read-in each SCF iteration. NoDirect is a synonym for Conventional.
OPTIONS RELATED TO CONVERGENCE AND CUTOFFS
Sets the SCF convergence criterion to 10-N. This is a density-based convergence criterion except for GVB and CASSCF, for which it is in terms of the orbital change and energy change, respectively.
Use modest integral accuracy early in direct SCF, switching to full accuracy later on. This is the default for direct SCF, and it can be turned off via NoVarAcc. VarInt is a synonym for VarAcc, and NoVarInt is a synonym for NoVarAcc.
Use normal, tight convergence in the SCF. This is the default. Synonymous with NoSinglePoint, NoSP, NoSleazy and TightIntegrals.
Requests the loose SCF convergence criteria appropriate for single points; equivalent to SCF=(Conv=4,VarInt,NoFinal,Direct). The default for single point CASSCF or direct SCF. Can be abbreviated SP. SinglePoint is a synonym for Sleazy.
Reduce cutoffs even further; uses Int=CoarseGrid and single-point integral accuracy during iterations, followed by a single iteration with the usual single point grid (MediumGrid). Not recommended for production quality calculations.
Symmetrize the density matrix at the first iteration to match the symmetry of the molecule (“initial density symmetrize”). NoIDSymm is the default.
Symmetrize the density matrix at every SCF iteration to match the symmetry of the molecule (“density symmetrize”). NoDSymm is the default. DSymm implies IDSymm.
Requests that all orbital symmetry constraints be lifted. It is synonymous with Guess=NoSymm and Symm=NoSCF.
Retain all symmetry constraints: make the number of occupied orbitals of each symmetry type (abelian irreducible representation) match that of the initial guess. Use this option to retain a specific state of the wavefunction throughout the calculation. It is the default only for GVB calculations.
Calls for the SCF procedure to account for integral symmetry by replicating the integrals using the symmetry operations. Allows use of a short integral list even if the wavefunction does not have the full molecular symmetry. Available for L502 (the default for RHF, ROHF and UHF) and L508 (SCF=QC).
Calls for the SCF procedure to account for integral symmetry (use of the petite integral list) by symmetrizing the Fock matrices. This is the default. FSymm is a synonym for FockSymm.
Save the wavefunction on the checkpoint file every iteration, so the SCF can be restarted. This is the default for direct SCF. NoSave suppresses saving the wavefunction.
Restart the SCF from the checkpoint file. SCF=DM cannot be restarted.
Sample Gaussian Input Files
Here are a number of sample Gaussian input files. All geometries have been optimized at the RHF/3-21G level of theory.
-----Cut Here----- # RHF/3-21G Dooh H2 0 1 H1 H2 H1 r1 r1 0.7348 -----Cut Here----- # RHF/3-21G Coov LiH 0 1 Li1 H1 Li1 r1 r1 1.6396 -----Cut Here----- # RHF/3-21G Dooh BeH2 0 1 X1 Be1 X1 1. H1 Be1 r1 X1 90. H2 Be1 r1 X1 90. H1 180. r1 1.3393 -----Cut Here----- # RHF/3-21G D3h BH3 0 1 B1 H1 B1 r1 H2 B1 r1 H1 120. H3 B1 r1 H2 120. H1 180. r1 1.1877 -----Cut Here----- # RHF/3-21G Td CH4 0 1 C1 H1 C1 r1 H2 C1 r1 H1 109.4712 H3 C1 r1 H1 109.4712 H2 120. H4 C1 r1 H1 109.4712 H2 -120. r1 1.0829 -----Cut Here----- # RHF/3-21G D*h CHCH 0 1 X1 C1 X1 r1 C2 X1 r1 C1 60. H1 C1 r2 X1 120. C2 180. H2 C2 r2 X1 120. C1 180. r1 1.1876 r2 1.0509 -----Cut Here----- # RHF/3-21G D2h CH2CH2 0 1 C1 C2 C1 r1 H1 C1 r2 C2 a1 H2 C1 r2 C2 a1 H1 180. H3 C2 r2 C1 a1 H1 180. H4 C2 r2 C1 a1 H1 0. r1 1.3149 r2 1.0736 a1 121.9078 -----Cut Here----- # RHF/3-21G D3d CH3CH3 0 1 C1 C2 C1 r1 H1 C1 r2 C2 a1 H2 C1 r2 C2 a1 H1 120. H3 C1 r2 C2 a1 H1 -120. H4 C2 r2 C1 a1 H1 60. H5 C2 r2 C1 a1 H4 120. H6 C2 r2 C1 a1 H4 -120. r1 1.5426 r2 1.0841 a1 110.7913 -----Cut Here----- # RHF/3-21G C3v NH3 0 1 X1 N1 X1 1. H1 N1 r1 X1 a1 H2 N1 r1 X1 a1 H1 120. H3 N1 r1 X1 a1 H1 -120. r1 1.0026 a1 106.3601 -----Cut Here----- # RHF/3-21G C*v CHN 0 1 X1 C1 X1 1. N2 C1 r1 X1 90.0 H1 C1 r2 X1 90.0 N2 180. r1 1.0502 r2 1.1372 -----Cut Here----- # RHF/3-21G Cs CH2NH 0 1 N1 C2 N1 r1 H1 N1 r2 C2 hnc1 H2 C2 r3 N1 hcn1 H1 180. H3 C2 r4 N1 hcn2 H1 0. r1 1.2565 r2 1.0147 r3 1.0747 r4 1.0802 a1 114.8980 a2 119.2306 a3 125.2900 -----Cut Here----- # RHF/3-21G Cs CH3NH2 0 1 N1 C2 N1 r1 H1 C2 r2 N1 a1 H2 C2 r3 N1 a2 H1 d1 H3 C2 r3 N1 a2 H1 -d1 H4 N1 r4 C2 a3 H1 d2 H5 N1 r4 C2 a3 H1 -d2 r1 1.4716 r2 1.0901 r3 1.0824 r4 1.0034 a1 114.7876 a2 108.9413 a3 113.6477 d1 121.4232 d2 64.2647 -----Cut Here----- # RHF/3-21G C2v OH2 0 1 O1 H1 O1 r1 H2 O1 r1 H1 a1 r1 0.9666 a1 107.6712 -----Cut Here----- # RHF/3-21G Cs CH3OH 0 1 O1 C2 O1 r1 H1 O1 r2 C2 a1 H2 C2 r3 O1 a2 H1 180. H3 C2 r4 O1 a3 H1 d1 H4 C2 r4 O1 a3 H1 -d1 r1 1.4411 r2 0.9658 r3 1.0787 r4 1.0850 a1 110.3279 a2 106.2600 a3 112.2625 d1 61.4330 -----Cut Here----- # RHF/3-21G C2v CH2O 0 1 O1 C2 O1 r1 H1 C2 r2 O1 a1 H2 C2 r2 O1 a1 H1 180. r1 1.0832 r2 1.2069 a1 122.5305 -----Cut Here----- # RHF/3-21G Cs CHOOH 0 1 C1 O1 C1 r1 O2 C1 r2 O1 a1 H1 C1 r3 O1 a2 O2 180. H2 O2 r4 C1 a3 O1 180. r1 1.1918 r2 1.3543 r3 1.0820 r4 0.9642 a1 122.5617 a2 123.6452 a3 114.7730 -----Cut Here----- # RHF/3-21G Dooh CO2 0 1 X1 C1 X1 1. O1 C1 r1 X1 90. O2 C1 r1 X1 90. O1 180. r1 1.1558 -----Cut Here----- # RHF/3-21G Coov FH 0 1 F1 H1 F1 r1 hf1 0.9375 -----Cut Here----- # RHF/3-21G C3v CH3F 0 1 F1 C1 F1 r1 H1 C1 r2 F1 a1 H2 C1 r2 F1 a1 H1 120. H3 C1 r2 F1 a1 H1 -120. r1 1.4040 r2 1.0795 a1 109.3911 -----Cut Here----- # RHF/3-21G Dooh F2 0 1 O1 O2 O1 r1 r1 1.4025 -----Cut Here----- # RHF/3-21G C2v CH2F2 0 1 X1 C1 X1 1. F1 C1 r1 X1 a1 F2 C1 r1 X1 a1 F1 180. H1 C1 r2 X1 a2 F1 90. H2 C1 r2 X1 a2 F1 -90. r1 1.3724 r2 1.0731 a1 54.4480 a2 124.0684 -----Cut Here----- # RHF/3-21G C3v CHF3 0 1 H1 C1 H1 r1 F1 C1 r2 H1 a1 F2 C1 r2 H1 a1 F1 120. F3 C1 r2 H1 a1 F1 -120. r1 1.0662 r2 1.3451 a1 110.6185 -----Cut Here----- # RHF/3-21G Td CF4 0 1 C1 F1 C1 r1 F2 C1 r1 F1 109.4712 F3 C1 r1 F1 109.4712 F2 120. F4 C1 r1 F1 109.4712 F2 -120. r1 1.325 -----Cut Here----- # RHF/3-21G Coov NaH 0 1 Na1 H1 Na1 r1 r1 1.9266 -----Cut Here----- # RHF/3-21G Dooh MgH2 0 1 X1 Mg1 X1 1. H1 Mg1 r1 X1 90. H2 Mg1 r1 X1 90. H1 180. r1 1.7261 -----Cut Here----- # RHF/3-21G D3h AlH3 0 1 Al1 H1 Al1 r1 H2 Al1 r1 H1 120. H3 Al1 r1 H2 120. H1 180. r1 1.5994 -----Cut Here----- # RHF/3-21G Td SiH4 0 1 Si1 H1 Si1 r1 H2 Si1 r1 H1 109.4712 H3 Si1 r1 H1 109.4712 H2 120. H4 Si1 r1 H1 109.4712 H2 -120. r1 1.4866 -----Cut Here----- # RHF/3-21G C3v PH3 0 1 X1 P1 X1 1. H1 P1 r1 X1 a1 H2 P1 r1 X1 a1 H1 120. H3 P1 r1 X1 a1 H1 -120. r1 1.4227 a1 120.8418 -----Cut Here----- # RHF/3-21G C2v SH2 0 1 S1 H1 S1 r1 H2 S1 r1 H1 a1 r1 1.3505 a1 95.8054 -----Cut Here----- # RHF/3-21G Coov ClH 0 1 Cl1 H1 Cl1 r1 r1 1.2935 -----Cut Here----- # RHF/3-21G Coov BrH 0 1 Br1 H1 Br1 r1 r1 1.4326 -----Cut Here----- # RHF/3-21G Coov IH 0 1 I1 H1 I1 r1 r1 1.6385 -----Cut Here----- # RHF/3-21G Cs CH3NO2 0 1 C1 N1 C1 r1 H1 C1 r2 N1 a1 H2 C1 r3 N1 a1 H1 d1 H3 C1 r3 N1 a1 H1 -d1 O1 N1 r4 C1 a2 H1 d2 O2 N1 r4 C1 a2 H1 -d2 r1 1.4928 r2 1.0795 r3 1.0743 r4 1.2402 a1 107.0223 a2 116.8778 d1 119.2261 d2 88.8732 -----Cut Here----- # RHF/3-21G D6h C6H6 0 1 C1 C2 C1 r1 C3 C2 r1 C1 120. C4 C3 r1 C2 120. C1 0. C5 C4 r1 C3 120. C2 0. C6 C5 r1 C4 120. C3 0. H1 C1 r2 C2 120. C3 180. H2 C2 r2 C3 120. C4 180. H3 C3 r2 C4 120. C5 180. H4 C4 r2 C5 120. C6 180. H5 C5 r2 C6 120. C1 180. H6 C6 r2 C1 120. C2 180. r1 1.3846 r2 1.0721 -----Cut Here----- # RHF/3-21G C2v C6H5F 0 1 X1 C1 X1 r1 C4 X1 r1 C1 60. C2 C1 r2 C4 a1 X1 90. C3 C4 r3 C1 a2 X1 -90. C5 C4 r3 C1 a2 X1 90. C6 C1 r2 C4 a1 X1 -90. F1 C1 r4 X1 120. C4 180. H2 C2 r6 C1 a3 C6 180. H3 C3 r7 C4 a4 C5 180. H4 C4 r5 X1 120. C1 180. H5 C5 r7 C4 a4 C3 180. H6 C6 r6 C1 a3 C2 180. r1 2.7475 r2 1.3741 r3 1.3847 r4 1.3587 r5 1.0712 r6 1.0695 r7 1.0713 a1 60.8497 a2 59.8573 a3 119.4057 a4 120.1070 -----Cut Here----- # RHF/3-21G D2h (para) C6H4F2 0 1 X1 C1 X1 r1 C4 X1 r1 C1 60.0 C2 C1 r2 C4 a1 X1 90. C3 C4 r2 C1 a1 X1 -90. C5 C4 r2 C1 a1 X1 90. C6 C1 r2 C4 a1 X1 -90. F1 C1 r3 X1 120. C4 180. H2 C2 r4 C1 a2 C6 180. H3 C3 r4 C4 a2 C5 180. F4 C4 r3 X1 120. C1 180. H5 C5 r4 C4 a2 C3 180. H6 C6 r4 C1 a2 C2 180. r1 2.7276 r2 1.3745 r3 1.3578 r4 1.0690 a1 60.6679 a2 119.5053 -----Cut Here----- # RHF/3-21G C2v (meta) C6H4F2 0 1 X1 C1 X1 r1 C4 X1 r1 C1 60. C2 C1 r2 C4 a1 X1 90. C3 C4 r3 C1 a2 X1 -90. C5 C4 r3 C1 a2 X1 90. C6 C1 r2 C4 a1 X1 -90. H1 C1 r4 X1 120. C4 180. F2 C2 r6 C1 a3 C6 180. H3 C3 r7 C4 a4 C5 180. H4 C4 r5 X1 120. C1 180. H5 C5 r7 C4 a4 C3 180. F6 C6 r6 C1 a3 C2 180. r1 2.7633 r2 1.3731 r3 1.3829 r4 1.0673 r5 1.0706 r6 1.3545 r7 1.0687 a1 59.1478 a2 60.3254 a3 118.8018 a4 121.6725 -----Cut Here----- # RHF/3-21G C2v (ortho) C6H4F2 0 1 C1 C2 C1 r1 C3 C2 r2 C1 a1 C4 C3 r3 C2 a2 C1 0. C6 C1 r2 C2 a1 C3 0. C5 C6 r3 C1 a2 C2 0. F1 C1 r4 C2 a3 C3 180. F2 C2 r4 C1 a3 C6 180. H3 C3 r5 C2 a4 C1 180. H4 C4 r6 C3 a5 C2 180. H5 C5 r6 C6 a5 C1 180. H6 C6 r1 C1 a4 C2 180. r1 1.2925 r2 1.3865 r3 1.3697 r4 1.3577 r5 1.0694 r6 1.0699 a1 121.0162 a2 120.0784 a3 120.2320 a4 117.8839 a5 120.5656 -----Cut Here----- # RHF/3-21G Cs C6H3F3 0 1 C1 C2 C1 r1 C3 C2 r2 C1 a1 C4 C3 r3 C2 a2 C1 0. C5 C4 r4 C3 a3 C2 0. C6 C5 r5 C4 a4 C3 0. F1 C1 r6 C2 a5 C3 180. F2 C2 r7 C3 a6 C4 180. H3 C3 r8 C4 a7 C5 180. F4 C4 r9 C5 a8 C6 180. H5 C5 r10 C6 a9 C1 180. H6 C6 r11 C1 a10 C2 180. r1 1.3749 r2 1.3696 r3 1.3745 r4 1.3728 r5 1.3825 r6 1.3537 r7 1.3504 r8 1.0673 r9 1.3538 r10 1.0683 r11 1.0689 a1 120.5441 a2 119.0015 a3 121.3610 a4 118.9105 a5 119.5234 a6 119.9060 a7 120.7900 a8 119.6953 a9 121.2759 a10 118.8179 -----Cut Here----- # RHF/3-21G C3v C6H3F3 0 1 C1 C3 C1 r1 C5 C3 r1 C1 60. C2 C5 r2 C1 30. C3 0. C4 C1 r2 C3 30. C5 0. C6 C3 r2 C5 30. C1 0. F1 C1 r3 C3 150. C5 180. H2 C2 r4 C4 150. C6 180. F3 C3 r3 C5 150. C1 180. H4 C4 r4 C6 150. C2 180. F5 C5 r3 C1 150. C3 180. H6 C6 r4 C2 150. C4 180. r1 2.3543 r2 2.7464 r3 1.3504 r4 1.0667