Proper correction for the basis set superposition error in SCF calculations of intermolecular interactions

Abstract

Abstract The effects of basis set extension to the space of the partner monomer in supermolecular SCF and perturbation calculations have been analysed for the model He2 and HeLi+ systems. In contrast to the suggestions of many authors it is demonstrated that the correction for the basis set superposition error should be calculated with the full basis set of the dimer without removing the occupied orbitals of the partner monomer. In fact, the enlargement of the monomer basis set by the partner occupied orbitals effectively improves the first-order exchange interaction energy. For the first-order electrostatic interaction energy any enlargement of a poor or medium size basis set of the monomer by the partner orbitals worsens its value. This work was partly supported by the Polish Academy of Sciences within the project MR.I.9. This work was partly supported by the Polish Academy of Sciences within the project MR.I.9. Notes This work was partly supported by the Polish Academy of Sciences within the project MR.I.9.