quickCBS is a program that can very easily calculate CBS extrapolated energy based on Gaussian, see http://sobereva.com/soft/quickCBS.

• To perform geometry optimization use the following keyword:

#p fopt CCSDT/aug-cc-pVTZ symm=loose freq

• To perform single point cal. use the following keyword:

#p CCSDT/aug-cc-pVTZ symm=loose

BSSE:

Each monomer in the dimer can steal basis function from the another interacting molecule. It lowers the energy of dimer in a way that’s not possible for isolated monomer leading to the overlapping of basis set when you compute energy.

A + B -> AB

EABInt. =EAB – EA - EB = Exothermicity or interaction energy

Stabilizing energy gives EABInt. < 0

Counterpoise Correction:-

BSSE is calculated by re-performing the whole cal. Using a mixed basis set, and the error is then subtracted a posteriori from the uncorrected energy.

EBSSE = (EA(AB)–EA(A)) + (EB(AB)–EB(B))

Using complete basis set (CBS) or infinite basis set :-

ECBS = EAB– EA–EB

EAB = EABInt. – BSSE - BSIE

BSIE :Basis set incompleteness error.

At infinity or complete basis set, BSSE =0

So, EAB = EABInt. – BSIE

quickCBS is a program that can very easily calculate CBS extrapolated energy based on Gaussian, see http://sobereva.com/soft/quickCBS.

See the paper

Article Online complete basis set limit extrapolation calculator

or the link

http://www.jamberoo.org/cbs/index.html