Gaussian 03 Online Manual
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.
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 H,1,RO1H,3,HOX3,2,-90.,0,1 X,2,1.,1,52.5,3,180.,0 H,2,RO2H1,6,H7OX,1,180.,0,2 H,2,RO2H2,6,H8OX,1,0.,0,2 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.