Enables and controls density fitting for the Coulomb problem for calculations involving pure (non-hybrid) DFT functionals. Density fitting basis sets are specified as part of the model chemistry within the job's route section. A list of built-in density fitting sets is included in the discussion of Basis Sets. DenFit is a synonym for this keyword.

Including this keyword causes a fitting set to be used if possible for the specified model chemistry. If no specific fitting set is specified in the route section, then the program will select the standard fitting set corresponding to the specified basis set, if one exists, or generate one automatically. When DensityFit is included in the Default.Route file, then /Fit is implied for all (relevant) calculations not specifying a fitting set.

The NoDensity keyword turns off the use of density fitting in pure DFT calculations. Since density fitting is off by default in the program, this keyword’s only use is to override any DensityFit in Default.Route. NoDenFit is a synonym for NoDensityFit.

If both a fitting set and NoDensityFit are included in a job’s route section, the latter is ignored, and density fitting is used.

#### Iterative

Controls whether a generalized inverse is formed or the fitting equations are solved iteratively. NonIterative is the default except for ADMP and PBC.

#### InvToler=N

Set the tolerance for a non-trivial eigenvalue of the generalized inverse of the fitting matrix to 10^{-N}.

#### Convergence=N

Specifies 10^{-N} as the convergence criterion for iterative solution of the fitting equations. Implies Iterative. The default is 10^{-6} for ADMP and 10^{-9} for BOMD.

#### Coulomb

Coulomb specifies the metric to be used for the fitting method. This is the default.

#### Overlap

Overlap specifies the metric to be used for the fitting method. The default is Coulomb.

#### JNormalization

Specifies that the read-in density basis has contraction coefficients corresponding to Coulomb normalization. This is the default.

#### AONormalization

Specifies that the read-in density basis has contraction coefficients corresponding to AO (overlap) normalization. JNormalization is the default.

Applies only to DFT calculations using pure (non-hybrid) functionals.