Counterpoise

Counterpoise corrections [Boys70, Simon96] may be computed using the Counterpoise keyword, which can be used in an energy calculation geometry optimization, frequency calculation or BOMD.

The Counterpoise keyword takes an integer value specifying the number of fragments or monomers in the molecular structure. We recommend the new syntax for defining fragments (see Overview of Molecule Specifications), and that is what is used in the examples.

Chapter 9 of Exploring Chemistry with Electronic Structure Methods [Foresman15, pp.440,442-44,454-56] provides an overview of counterpoise corrections including several examples.

NewGhost

Requests new-style ghost atoms for which integration grid points for DFT quadrature are included. NewBq is a synonym for NewGhost. This is the default and the recommended method.

OldGhost

Requests old-style ghost atoms. OldBq is a synonym for OldGhost. This option is only useful for comparison with previous results.

Cannot be used with ONIOM or SCRF. Counterpoise calculations cannot produce molecular orbitals.

Counterpoise Input. The following input is an example of a counterpoise calculation:

# UB3LYP/6-31G(d) Counterpoise=2 

Counterpoise on water dimer

1,2 1,2 0,1
O(Fragment=1)  0.00  0.00  0.00
O(Fragment=2)  0.00  0.00  2.98
H(Fragment=1)  0.49  0.76 -0.29
H(Fragment=1)  0.49 -0.76 -0.29
H(Fragment=2) -0.91  0.00  3.24
H(Fragment=2) -0.01  0.00  2.03

The preceding job also illustrates the use of fragment-specific charge and spin multiplicity specifications. The first pair on the charge and spin line gives the values for the molecule as a whole; they are followed by the charge and spin for each fragment in fragment number order.

Here is an example counterpoise optimization using ECPs:

# B3LYP/LANL2DZ Counterpoise=2 NoSymm Opt 
 
HBr + HF, optimization with counterpoise correction using ECP basis
 
0 1 0 1 0 1
H(Fragment=1)    0.00000000   0.00000000   0.58022808 
Br(Fragment=1)   0.00000000   0.00000000  -0.83659185
F(Fragment=2)    0.00000000   0.00000000   2.77788358
H(Fragment=2)    0.00000000   0.00000000   3.69953441

Counterpoise Output. Typical output from a Counterpoise calculation follows:

 ounterpoise corrected energy =    -622.483714884838
                  BSSE energy =       0.005664641553
             sum of fragments =    -622.333463706103
          complexation energy =     -97.84 kcal/mole (raw)
          complexation energy =     -94.28 kcal/mole (corrected)

These lines give the counterpoise corrected energy and basis set superposition errors, respectively.