Generalized molecular orbital theory: Ground state and ionization potentials of water and dinitrogen

Abstract

Generalized molecular orbital (GMO) theory is a limited multiconfiguration self-consistent field (MCSCF) procedure, which provides a simple means of obtaining a set of optimized primary orbitals for use in configuration interaction (CI) calculations. Results for the ground states of H2O and N2 show that the most important GMO orbitals are nearly identical to the natural orbitals from large CI calculations. For H2O, our GMO-CI correlation energy is only 4 mhartrees less than that obtained from an identical CI with the most important natural orbitals. The GMO theory for doublet states provides a facile means of obtaining accurate ionization potentials (IPS) from small CI calculations (30–60 configurations). For the first three IPS of H2O the error is less than 0.5 eV while for the first two IPS of N2 the error is less than 0.1 eV.