Gaussian to Q-Chem: A Stationary
Jiawei Xu and Yunlong Shang
Released: 2022-03-17 / Updated: 2022-06-16
This stationary is aimed to help Gaussian users to get familiar with common input keywords in Q-Chem.
Developers: Jiawei Xu and Yunlong Shang
Acknowledgement: We thank Prof. Haiyan Wei from Nanjing Normal University for her advice, computation resources and support in software.
Part I. Job Settings
| Keywords for Gaussian | Notes for Gaussian | Keywords for Q-Chem | Notes for Q-Chem |
|---|---|---|---|
| –Link1– | Need one blank line before. | @@@ | |
| %Mem=[Memory] | Mem_Total N Mem_Static N | Default: 8000 MB Default: 64 MB for AO integrals. | |
| %Chk=[filename].chk | Save binary checkpoint file. | GUI 2 or IQMol_FChk True | Save formatted checkpoint file. |
Part II. Basic Keywords
| Keywords for Gaussian | Notes for Gaussian | Keywords for Q-Chem | Notes for Q-Chem |
|---|---|---|---|
| NoSymm | Do not use symmetry to accelerate and do not reorient molecule to standard orientation. | (1) Symmetry True/False (2) Sym_Ignore True/False (3) Sym_Tol N (4) Symmetry_Decomposition N | (1) Default: True. Use symmetry in calculation. (2) Default: True. Decide whether to reorient molecule. (3) Default: 5. Tolerance for point group: 10-N. (4) Default: 1. Calculate MO symmetry. |
| HF | Method HF | Hartree-Fock method. | |
| [functional name] | Density functional theory. | (1) Method [functional name] (2) Exchange [functional name] (3) Correlation [functional name] | Density functional theory. Exchange and correlation enable use of generic definition of functional. |
| [basis set name] | Basis [basis set name] | ||
| Integral=Grid=[grid setting] | Fine: 75,302. UltraFine: 99,590; Default in G16. SuperFine: 175,974 (H/He); 250,974 (Else). | XC_Grid N | Default: 2 (Fine) for meta-GGAs and B95-, B-97 based; 3 (UltraFine) for Minnesota functionals. Alternative to SuperFine in Gaussian: XC_Grid 000175000974 / 000250000974 |
| R/U[HF or functional name] | If not explicit, restricted shell is default for singlet state and unrestricted for else. | Unrestricted True/False | Same default with Gaussian. |
| RO[HF or functional name] | Restricted open-shell Hartree-Fock (ROHF) or Kohn-Sham (ROKS). | Method HF or [functional name] Unrestricted False | For non-singlet systems only. |
| Guess=Read | SCF_Guess Read | ||
| Geom=AllCheck | Read | (in $Molecule section) | |
| Out=wfn | Read extra input for .wfn filename from end of input file. | Write_wfn filename | |
| SCF=Conver=N | Default: 8 (Synonym: SCF=Tight) | SCF_Convergence N | Default value is related to jobtype. (10–N for RMS and 10-(N-2) for density) |
| SCF=MaxCycle=N | Default: 128 | SCF_Max_Cycles N | Default: 50. The default value may be too small for some systems. |
| SCF=VShift=N | Default: 100. Level shift: N/1000 a.u. | Step_Epsilon N | Default: 10. Level shift: N/100 a.u. |
| SP | Singlet point. (This is default when no job type is specified.) | JobType Energy | Singlet point. (This is default when no job type is specified.) |
Part III. Keywords for Specific Job Type
III.1 Optimization and PES Scan
| Keywords for Gaussian | Notes for Gaussian | Keywords for Q-Chem | Notes for Q-Chem |
|---|---|---|---|
| Opt | JobType Opt | ||
| Opt=TS | JobType TS | ||
| Opt=ModRedundant | Read extra input after coordinates. | JobType PES_Scan | (In $Scan section) Stre [A1] [A2] Start End Increment Bend [A1] [A2] [A3] Start End Increment Tors [A1] [A2] [A3] [A4] Start End Increment |
| Scan | JobType PES_Scan (in $Scan section) Frozen_Scan True/False | Default: False (do not freeze). | |
| Opt=[initial Hessian] | (1) CalcFC: calculate Hessian matrix at the first step of geometry optimization. (2) ReadFC: read initial Hessian from .oldchk or .chk file. | Geom_Opt_Hessian [initial Hessian] | (1) Default: Diagonal. This is a special method in Q-Chem for cheap Hessian matrix at the first step. (2) Read: read pre-calculated Hessian. |
| Opt=[coordinates] | (1) Cartesian (2) Z-Matrix | Geom_Opt_Coords [coordinates] | (1) Default: -1. Switch to Cartesian if internal coordinates fails. (2) 0: Cartesian. (3) 1: Z-matrix |
| Opt=[convergence] | (1) Loose (2) Tight (3) VeryTight | Geom_Opt_Tol_Gradient N Geom_Opt_Tol_Displacement N Geom_Opt_Tol_Energy N | (1) Default: 300 (Tolerance: N×10-6 a.u.) (2) Default: 1200 (Tolerance: N×10-6 a.u.) (3) Default: 100 (Tolerance: N×10-8 a.u.) |
| Opt=MaxCycles=N | Geom_Opt_Max_Cycles N | Default: 50. The default value may be too small for some systems. | |
| Opt=MaxStep=N | Max step size: N×10-2 Bohr. | Geom_Opt_DMax N | Default: 300. Max step size: N×10-3 Bohr. |
| NoSymm | Geom_Opt_SymFlag True/False | Default: True. Control whether to track symmetry only in geometry optimization. | |
| Opt=GDIIS | Geom_Opt_Max_DIIS N | Default: 0 (Do not use DIIS.). | |
| Freq=NFreq=N | This is only available for ONIOM. | Geom_Opt_ChaRac True/False | Default: False. Better to be set as True in TS optimization. |
III.2 Excited State Methods
| Keywords for Gaussian | Notes for Gaussian | Keywords for Q-Chem | Notes for Q-Chem |
|---|---|---|---|
| CIS | Method HF | When CIS_N_Roots is set to non-zero. | |
| TD | Method [functional name] | When CIS_N_Roots is set to non-zero. | |
| CIS/TD(NStates=N) | Default: 3. | CIS_N_Roots N | No default so must be specified. |
| CIS/TD(Root=N) | Default: 1. | CIS_State_Deriv N | No default so must be specified. |
| CIS/TD(Singlet) | This is default. Note that singlet and triplet only work for closed-shell systems or other spin-adapted methods. | CIS_Singlets True/False | Default: True |
| CIS/TD(Triplet) | CIS_Triplets True/False | Default: True | |
| CIS/TD(NStates=N,50-50) | Search for N singlet states and N triplet states. | There is no such keyword in Q-Chem. | |
| Density=Current | CIS_Relaxed_Density True/False | Default: False. | |
| Max_CIS_Cycles N | Default: 30. The default value may be too small for some systems. | ||
| CIS_Convergence N | Default: 6 (Threshold for convergence 10–N) | ||
| Default: 2×NStates | CIS_Subspace N | Default: As many as required. |
Part IV. Special Functions in Q-Chem
IV.1 Spin-Flip TDDFT
| Keywords | Notes |
|---|---|
| Spin_Flip True/False | Default: False. SF-TDDFT in Q-Chem is flip-down framework. Although available theoretically, flip-up framework is not currently supported in Q-Chem. ROKS ground state is not supported in Q-Chem. (It is available in GAMESS.) |
| CIS_S2_Thresh N | Default: 120 (Threshold for <S2> of singlet state: N/100) |
| SASF_RPA True/False | Default: False. To perform spin-adapted SF-TDDFT. Although reference state is open-shell, excited states remain eigenfunctions of S2 operator so no spin contamination. Analytical derivative is not currently available for SA-SF-TDDFT. |
IV.2 Minimum Energy Crossing Point Search
| Keywords | Notes |
|---|---|
| JobType Opt MECP_Opt True | Perform MECP search. Since this is a optimization job, options for JobType Opt can also influence MECP search. |
| MECP_Methods [method] | Default: Branching_Plane (Branching plane updating method, BPUPD). Direct: Calculate gradient difference vector and derivative coupling vectors directly. This needs to calculate non-adiabatic coupling, which can be time-consuming. Penalty_Function: Use penalty function method to accelerate convergence when geometry is far from MECP structure. |
| MECP_State1 [[Spin],[State_Deriv]] MECP_State2 [[Spin],[State_Deriv]] | Specify two states for MECP search. For example, MECP_State1 [0,1] involves S1 state in MECP search. To involve ground state, set State_Deriv to 0. |