This section describes DFT-C,[Witte et al.(2017b)Witte, Neaton, and Head-Gordon] an empirical correction for basis set superposition error (BSSE) in DFT calculations that is an adaptation of Grimme’s geometrical counterpoise (gCP) correction.[Kruse and Grimme(2012)] Unlike the traditional Boys-Bernardi counterpoise correction (Section 8.8),[Boys and Bernardi(1970)] 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 *intra*molecular BSSE. The form of this correction is

(5.54) |

where is a damped, pairwise BSSE correction,

(5.55) |

The quantity

(5.56) |

is the undamped pairwise BSSE and

(5.57) |

is a damping function. The quantity is a many-body correction to the two-body BSSE correction, given by

(5.58) |

where

(5.59) |

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 *$rem* variable DFT_C; to invoke the DFT-C method, simply add this to your input:

DFT_C TRUE

The DFT-C method can be applied to any local, GGA, or meta-GGA density functional, as in the following example.

**Example 5.54** Geometry optimization of the methane dimer using B97M-V-C/def2-SVPD, *i.e.*, the B97M-V functional with the DFT-C BSSE correction in the def2-SVPD basis set.

$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

DFT_C

Controls whether the DFT-C empirical BSSE correction should be added.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE

(or 0) Do not apply the DFT-C correction

TRUE

(or 1) Apply the DFT-C correction

RECOMMENDATION:

NONE