Pariser–Parr–Pople method

The Pariser-Parr-Pople method applies semi-empirical quantum mechanical methods to the quantitative prediction of electronic structureand spectra, in molecules of interest to chemists. Previous methods existed, such as Hückel's rule, but were limited in their scope, application and complexity, as is the Extended Hückel's rule.

This approach was developed in the 1950s by Rudolph Pariser with Robert Parr and co-developed by John Pople. 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 a Zero Differential Overlap (ZDO) approximation to reduce the problem to reasonable size and complexity but still required modern solid state computers (as opposed to puch-card or vacuum tube systems) before becoming fully useful for molecules larger than benzene.

Interestingly enough, Pariser's goal of using this method to predict the characteristics of complex oganic dyes was never realized. The method has wide applicability in precise prediction of electronic transitions, particularly lower singlet transitions, and found wide application in theoretical and applied quantum chemistry. 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.