Basic formulas for a semiempirical zero differential overlap method called the fragment self-consistent field theory are summarized, which is designed for the determination of wavefunctions for very large molecular systems. The molecule is partitioned into a subsystem where important chemical changes (geometry distortion, bond fission, electronic excitation) take place, and an environment not altered by these events but having an effect on them. The novelty of the theory is in the use of nonorthogonal strictly localized molecular orbitals allowing an unequivocal and chemically relevant definition of the subsystem. The method has been implemented both at the complete neglect of differential overlap and modified neglect of diatomic overlap levels. For the latter an approximation for the diatomic interaction integrals has been proposed, which seems to bring a substantial reduction in computational time. © 1992.
Náray-Szabó, G., & Ferenczy, G. G. (1992). Molecular wavefunctions from chemical bonds: the fragment self-consistent field theory. Journal of Molecular Structure: THEOCHEM, 261(C), 55–62. https://doi.org/10.1016/0166-1280(92)87064-7