Molecular Mechanics Methods
Last Update: 12/31/2000

There are three molecular mechanics methods available in Gaussian 98. They are designed for use in ONIOM calculations, but they are also available as independent methods. No basis set keyword should be specified with these keywords.

The following force fields are available:

Amber: The Amber force field as described in [325]. The actual parameters (parm96.dat) have been updated slightly since the publication of this paper. We use the current version from the Amber web site (www.amber.ucsf.edu).

DREIDING: The DREIDING force field as described in [328].

UFF: The UFF force field as described in [326]. UFF uses charges calculated by the method of charge equilibration [327].

Amber calculations require that all atom types be explicitly specified using the usual Amber notation within the normal molecule specification section:

       C-CT	        Specifies an SP3 aliphatic carbon atom.
            C-CT-0.32	   Specifies an SP3 aliphatic carbon atom with a partial charge of 0.32.
            O-O--0.5	    Specifies a carbonyl group oxygen atom with a partial charge of -0.5.

Consult the Amber paper for definitions of atom types and their associated keywords.

UFF and DREIDING may also optionally provide atom typing information within the molecule specification, using the type keyword conventions of those methods. If no atom typing information is provided, the program will attempt to determine atom types automatically.

Note: The GaussView package specifies correct atom types automatically for all atoms when it sets up a Gaussian calculation involving a molecular mechanics method.

Analytic energies and gradients and numerical frequencies.

ONIOM ONIOM

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