Page "Robert Parr" Paragraph 2

Working with DuPont chemist Rudolph Pariser, Parr developed a method of computing approximate molecular orbitals for pi electron systems, published in 1953.

Since an identical procedure was derived by John A. Pople the same year, it is generally referred to as the Pariser-Parr-Pople method or PPP method.

The PPP method differed from existing structural chemistry thinking ( which advocated maximum overlap principle ) by advancing the concept of zero differential overlap approximation.