10.7.1 Counterpoise calculations

Counterpoise corrections are easily performed using dummy cards. One first computes the energy of the total system, and then for the subsystems using dummy cards. The process can, however, be automated using the command

COUNTERPOISE [, key1=value, key2=value,......]

Without any options, this will calculate the ghost-orbital corrections to dimer interaction energies using the last energy calculation to define the dimer and the methods to be used. First of all, the molecule is automatically partitioned into two optimally separated fragments. This is done by finding the partitioning that has the largest minimum distance between any pair of atoms in different fragments. Optionally, one may give the option SEPARATION=distance; if the optimum fragment separation is smaller than distance, then it will be assumed that the system is not a non-bonded complex, and the counterpoise calculation will not be done at all. This gives support for running the same Molpro input for both dimers and monomers.

The counterpoise procedure performs four calculations. For each of the identified monomers, it calculates the energy at the dimer geometry using first the dimer basis set, and secondly just the basis functions tied to the monomer atoms. The difference between these, the counterpoise correction, is reported, and added to the previously-calculated dimer energy.

Further options that specify the calculation to be run can be specified exactly as for geometry optimisations; see section 46.1.1 for further details.

molpro@molpro.net 2018-12-18