Gaussian 03 Online Manual
Last update: 2 October 2006


Counterpoise corrections [433,434] may be computed using the Counterpoise keyword, which can be used on an energy calculation, optimization or frequency calculation or BOMD.

The Counterpoise keyword takes an integer value specifying the number of fragments or monomers in the molecular structure. The facility also requires an additional integer to be placed at the end of each atom specification indicating which fragment/monomer it is part of.

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.

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

Counterpoise Input. Here are examples using a Z-matrix (left) and Cartesian coordinates (right):

# MP2/6-31G Counterpoise=2 Opt          # MP2/6-31G Counterpoise=2 Opt 

Counterpoise with Z-matrix              Counterpoise with Cartesian 

0,1,0,3,1,2                             0,1 
O,0.0,0.0,0.0,1 structures begin here   1 0.00 0.00 0.92 1 
O,1,ROO,2                               9 0.17 0.00 2.73 2 
X,1,1.,2,X3O                            1 0.77 0.00 3.43 2 
H,1,RO1H,3,HOX3,2,90.,0,1               9 0.00 0.00 0.00 1 

Z-matrix variables... 

Note that the Z-matrix input requires a 0 after the dihedral angle value/variable (to indicate that the final angle is a dihedral) prior to the fragment number. Also, the first atom in the Z-matrix must be given in Cartesian coordinates. Clearly, using Cartesian coordinates for such jobs makes specifying fragment numbers in the input much more straightforward.

The preceding Z-matrix also illustrates the use of fragment-specific charge and spin multiplicity specifications. The format of the corresponding input line in this case is:

total-charge, total-spin, frag. 1-charge, frag.1 multiplicity, frag. 2 charge, frag. 2 multiplicity

An example counterpoise optimization using ECPs:

# hf/lanl2dz counterpoise=2 nosymm opt test 

HBr + HF, optimization with counterpoise correction using ECP basis 

0 1 
H   -0.046866  0.   0.586860   1 
Br  -0.331864  0.  -0.801000   1 
F    0.396755  0.   2.739275   2 
H    0.584835  0.   3.641534   2

Counterpoise Output. Here is some sample output from a Counterpoise calculation:

Counterpoise: corrected energy =  -2660.083831739527 
Counterpoise: BSSE energy =      0.003902746890 

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