[1][2] [3] It is essentially a more efficient method of finding reasonable approximations of molecular orbitals, useful in predicting physical and chemical nature of the molecule under study since molecular orbital characteristics have implications with regards to both the basic structure and reactivity of a molecule.
This method used the zero-differential overlap (ZDO) approximation to reduce the problem to reasonable size and complexity but still required modern solid state computers (as opposed to punched card or vacuum tube systems) before becoming fully useful for molecules larger than benzene.
Originally, Pariser's goal of using this method was to predict the characteristics of complex organic dyes, but this was never realized.
The two basic papers on this subject were among the top five chemistry and physics citations reported in ISI, Current Contents 1977 for the period of 1961–1977 with a total of 2450 references.
In contrast to the Hartree–Fock-based semiempirical method counterparts (i.e.: MOPAC), the pi-electron theories have a very strong ab initio basis.