GerritJan Linker

Counterpoise in MOLCAS To perform the Counterpoise procedure in MOLCAS the charge parameter can be used in the basisset definition in the SEWARD input to make dummy or ghost atoms. These are placeholders for basisfunctions only. They are input as normal atoms but with the charge of the atoms set to 0. They will therefore not generate a field due to the nuclear charge. The Counterpoise procedure is used to calculate the bonding energy of a system AB. When calculating the AB system and the A and B system separately the bonding energy cannot be calculated simply as E_{bonding} = E_{AB}  (E_{A}+E_{B}) The reason is that in the AB system, fragment A is described in the complete basis of A and B. The same applies for B. In AB the basisset is larger for the subsystems than in the isolated systems A and B. This is the so called basisset superposition error (BSSE) for which we need to correct. The procedure is to calculate fragment A in the complete basis of AB and to do the same for fragment B. The thus obtained energies for A and B can then be used in the above formula to compute the bonding energy. AB, A and B are all 3 calculated in the same basis. To perform this procedure is to set the charge to 0 in the basisset definition in SEWARD. Example: Basis set Ni.Uncontracted...4s4p4d. / AUXLIB Nix 0.00000 0.00000 0.000000 Bohr Charge 0.0 End of basis
