The first step in producing a Gaussian input file is to build the desired molecule. The bond lengths, bond angles, and dihedral angles for the molecule will be used by GaussView to write a molecular structure for the calculation. Once this is completed, you can use the Calculation=>Gaussian menu path to open the Gaussian Calculation Setup dialog. It is illustrated in Figure 46.
Figure 46. The Gaussian Calculation Setup Dialog
This dialog allows you to set up virtually all types of Gaussian calculations
and to submit them from GaussView. The route section that GaussView is generating
appears at the top of the dialog, and it is constantly updated as you make selections
in the dialog.
The Gaussian Calculation Setup dialog contains several panels, described individually below. The buttons at the bottom of the dialog have the following effects
Submit: Starts a Gaussian calculation using the current input file. You will be prompted to save the input file if you have not already done so.
Cancel: Closes the dialog box and returns all selections to their default values.
Edit: Allows direct access to the input file with an external text editor. The input file is not available for editing until it has been saved with GaussView.
Retain: Closes the dialog box. Current selections are retained but the input file is not created/updated, and no Gaussian job is submitted.
Defaults: Returns all items to their default values.
Help: Provides on-line help for this dialog box.
The Gaussian Setup preferences dialog may be used to specify defaults for the Gaussian Calculation Setup dialog. Click the Calculation button, and then specify the desired settings for future Gaussian calculations. These will be applied to future job setup operations.
The Job Type panel also appears in Figure 46. The top popup menu selects the job type. The default is a single point energy calculation. The remaining fields in the panel represent common options for the selected job type (the figure shows the ones for an Opt Freq calculation).
In order to select a different job type than those listed in the popup menu, select the blank menu item at the bottom of the list, and then type the appropriate Gaussian keyword into the Additional Keywords section in the lower section of the dialog.
You can also use this field to add any desired Gaussian keyword and/or option. In the latter case, you must repeat the keyword within this field even if it already appears in the route section. GaussView will merge all options for the same keyword within the route section (see Figure 47 for an example). Note that this area is designed only for adding keywords to the route section. Use the Edit button for creating complex input files.
Figure 47. Adding an Option via the Additional Keywords Field
This window illustrates GaussView's ability to merge options from dialog
controls and ones typed into the Additional Keywords field. Here, we've added
the Internal option to the IRC keyword, while another option has been generated
with the Calculate Force Constants popup selection.
The Method panel specifies the quantum mechanical method to be used in a calculation. The default method is a ground state, closed shell Hartree-Fock calculation using the 3-21G basis set. This panel is illustrated in Figure 48.
Figure 48. The Method Panel
The Method panel is where the model chemistry for the calculation is specified.
The fields in the Method line specify the following items
Whether the calculation is for a ground state or an excited state.
The theoretical method. For some choices, the fourth field is used to select the specific method of the given type. For example, in Figure 48, the method field is set to DFT, and the fourth field selects the B3LYP functional.
The wavefunction type (closed shell vs. open shell). The default is an unspecified type. The Restricted, Unrestricted, and Restricted-Open selections prepend R, U and RO to the method keyword (respectively).
The Basis Set menus allow the selection of the basis set to be used in the calculation. Polarization functions and diffuse functions may be added to the basis set using the corresponding menus in this line. Select the blank item at the bottom of the basis set menu to select a basis set other than those that can be constructed via the controls in this area. You may enter any basis set keyword in the Additional Keywords area.
The Charge and Spin fields specify the molecule's charge and spin multiplicity. GaussView will select values for these fields based on the molecular structure. They may be modified as needed.
The Title panel holds a field used for the Gaussian title section (designed to contains a brief description of the job). Type your description into the text box.
The Link 0 panel is used for entering Link 0 commands for the job (see Figure 49). Be sure to name the checkpoint file if you intend to visualize output from this job. You can use the Checkpoint File button to specify its location by browsing.
Figure 49. The Link 0 Panel
This panel specifies a name for the checkpoint file and also the amount of
memory to use for this job.
The NBO panel is used to select NBO analysis at the conclusion of the Gaussian job. It is illustrated in Figure 50. The Type menu specifies the kind of NBO analysis to perform. The Checkpoint Save field allows you to save NBOs in the checkpoint file for later visualization (the default is Don't Save).
Figure 50. The NBO Panel
The panel specifies the type of NBO analysis and which NBOs to save in the
checkpoint file. The selection in this window is often a useful one when you
will use them to generate an active space for a CASSCF calculation.
The Solvation panel allows you to specify that the calculation is to be performed in solution rather than in the gas phase. It is illustrated in Figure 51. The Model field allows you to specify a specific solvation model (the default is PCM, which itself defaults to IEFPCM). You can also specify the solvent by selecting it from the corresponding popup menu. Use the Other selection to select a solvent other than those on the list. The dielectric field will then become active.
Figure 51. The Solvation Panel
This panel specifies the SCRF model to use for solvent effects. The Default
selection corresponds to SCRF=PCM.
Note that some solvation models may present different/additional fields for their required parameters.
The General panel allows you to select some commonly used general calculation options. It is illustrated in Figure 52.
Figure 52. Selecting General Gaussian Options
This panel contains a set of commonly used options. This window illustrates
the defaults.
The following table indicates the Gaussian keywords corresponding to these items
| Option | Default | Keyword |
| Use Quadratically Convergent SCF | Off | SCF=QC |
| Use Modified Redundant Coordinates | On | Geom=ModRedundant |
| Ignore Symmetry | Off | NoSymm |
| Additional Print | Off | #P |
| Write Connectivity | On | Geom=Connectivity |
The Use Modified Redundant Coordinates item is enabled only if you have set up redundant coordinates with the Redundant Coordinate Editor. If not, the item is ignored (despite its default value).
The Write Connectivity option also includes the appropriate additional input section(s) within the Gaussian input file.
Note: The default SCF algorithm has changed with Gaussian 03, and we have new recommendations for the few remaining problem cases (SCF=QC is not always the best next choice). Consult the discussion of the SCF keyword in the Gaussian 03 User's Reference for details.
TheGuess panel contains settings related to the initial guess. It is illustrated in Figure 53. Consult the discussion of the Guess keyword in the Gaussian 03 User's Reference for full details on these options.
The Guess Method popup specifies the type of initial guess to use. It has the following options:
Default: Uses the Gaussian 03 default initial guess.
Core Hamiltonian: Uses the Gaussian 98 default initial guess. Not recommended unless only Gaussian 98 is available.
Extended Huckel: Uses the Huckel guess (Guess=Huckel).
Read checkpoint file: Retrieves the initial guess from the checkpoint file (Guess=Read).
Figure 53. Gaussian Initial Guess Options
This window shows the default settings for the initial guess.
The options in this panel have the following meanings
| Option | Default | Keyword |
| Mix HOMO & LUMO in initial guess | Off | Guess=Mix |
| Only do guess (no SCF) | Off | Guess=Only |
| Save orbitals to checkpoint file | Off | Guess=Save |
| Always generate guess in optimizations | Off | Guess=Always |
| Localize orbitals | Off | Guess=Local |
| Permute orbitals from MOs Dialog | On | Guess=Permute |
The Permute orbitals for MOs Dialog is disabled unless you have specified an alternate orbital ordering with the MO Editor. If enabled, it is on by default.
The PBC panel is used to specify options to the Gaussian PBC keyword (see Figure 54). Checking the Use PBC box causes the translation vectors to be added to the molecule specification. This is the default when a unit cell has been defined with the Crystal Editor. The panel is disabled for non-periodic systems.
Figure 54. The PBC Panel
The Use PBC checkbox causes the translation vectors to be placed in the molecule
specification.