Modification of Roothaan Equations for the Ab-Initio Calculation of Interactions in Large Molecular Systems in the Absence of Basis Set Superposition Error

Roothaan equations have been modified in a previous work with the aim of avoiding BSSE at the Hartree-Fock level of theory. The resulting scheme, called SCF-MI (Self Consistent Field for Molecular Interactions), underlines its special usefulness for the computation of intermolecular interactions. In the present work we present the generalisation of the theory to the case of K interacting fragments one of which may be described by an open shell configuration. Applications to large molecular cluster systems are presented and discussed.