The Guess Panel

The Guess panel contains settings related to the initial guess. It is illustrated below. Consult the discussion of the Guess keyword in the Gaussian 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:

g_guess.tif
Gaussian Initial Guess Options

The checkboxes in this panel have the following meanings:

Option
Default
Keyword
Mix HOMO & LUMO orbitals
Off
Guess=Mix
Only do guess (no SCF)
Off
Guess=Only
Save orbitals to checkpoint file
Off
Guess=Save
Use fragments (atom groups) for generating guess
Off
Guess=Fragment
Always generate guess in optimizations
Off
Guess=Always
Localize orbitals
Off
Guess=Local
Permuted orbitals from MOs Dialog
On
Guess=Permute

The Permuted 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 Use fragments (atom groups) for generating guess is disabled unless fragments have been defined using the Atom Group Editor. If enabled, it is checked by default. In addition, fragment-specific charges and spin multiplicities are generated and placed into the route section. You can also modify them using the Atom Group Editor (see the example for antiferromagnetic coupling in a later section of this manual).

See here for a list of equivalent G16 Keywords for Gaussian Calc. Setup selections.