This section describes DFT-C,997 an empirical correction for basis set superposition error (BSSE) in DFT calculations that is an adaptation of Grimme’s geometrical counterpoise (gCP) correction.493 Unlike the traditional Boys-Bernardi counterpoise correction (Section 8.8),110 the cost of the DFT-C correction is essentially zero (on the scale of a DFT calculation), and the latter provides an estimate of both inter- and intramolecular BSSE. The form of this correction is
where is a damped, pairwise BSSE correction,
is the undamped pairwise BSSE and
is a damping function. The quantity is a many-body correction to the two-body BSSE correction, given by
The parameters , , , and are basis-set-dependent, and the overall scaling parameter is loosely method-dependent. All of these parameters are set internally based on the method and basis $rem specifications.
Note: Currently, only the def2-SVPD basis set is supported for use with DFT-C.
The DFT-C correction is governed by the following $rem variable:
The DFT-C method can be applied to any local, GGA, or meta-GGA density functional, as in the following example.
$molecule 0 1 C 0.000000 -0.000140 1.859161 H -0.888551 0.513060 1.494685 H 0.888551 0.513060 1.494685 H 0.000000 -1.026339 1.494868 H 0.000000 0.000089 2.948284 C 0.000000 0.000140 -1.859161 H 0.000000 -0.000089 -2.948284 H -0.888551 -0.513060 -1.494685 H 0.888551 -0.513060 -1.494685 H 0.000000 1.026339 -1.494868 $end $rem JOBTYPE opt BASIS def2-SVPD METHOD b97m-v DFT_C true $end