MOLECULAR ORBITALS FOR LARGE MOLECULES .V. PARAMETERIZATION FROM SCF MATRICES OF RELATED SMALL MOLECULES

A new method for obtaining molecular orbitals in large molecules is described within the LCAO framework. After evaluation of overlap and kinetic integrals exactly, parameters are obtained from self-consistentfield calculations on small, chemically similar molecules for the potential-energy parts of the SCF matrices. These parameters are employed to generate both nonzero and zero overlap matrix elements of the large molecule of known geometry. No experimental parameters are introduced, and all electrons are included. Given the parameters (many are tabulated), the Hamiltonian matrix is readily constructed, so that very large systems (40 atoms and 140 AO's) can be handled. Total energies, eigenvalues, overlap populations, atomic charges, and dipole moments are compared with results from rigorous SCF calculations.