Keywords for Modules GRAD and RDGRAD

Many of the dscf and ridft keywords are also used by grad and rdgrad.

 
$drvopt

This keyword and corresponding options are required in gradient calculations only in special circumstances. Just $drvopt is fine, no options needed to compute derivatives of the energy with respect to nuclear coordinates within the method specified: SCF, DFT, RIDFT.

If running a DFT gradient calculation, it is possible to include the derivatives of the quadrature weights, to get more accurate results. In normal cases however those effects are marginal. An exception is numerical calculation of frequencies by Numforce, where it is strongly recommended to use the weight derivatives option. The biggest deviations from the uncorrected results are to be expected if doing gradient calculations for elements heavier than Kr using all electron basis sets and very small grids. To use the weight derivatives option, add

weight derivatives

in $dft.

The option

point charges

in $drvopt switches on the evaluation of derivatives with respect to coordinates of point charges. The gradients are written to the file $point_charge_gradients old gradients will be overwritten.