Molecular orbital Pariser-Parr-Pople approximation

Even if some interesting applications of the GHF-method had been found in solid-state theory [23,24], the applications to molecular systems were comparativlely few [40]. One major application to molecular systems had been worked out by Fukutome [40], and it was a study of the properties of the polyacetylene by means of the Pariser-Parr-Pople (PPP) approximation. It seemed hence desirable to make a molecular study based on ab-inttU) calculations to verify that one would get similar results and to get some experience in handling general Hartree-Fock orbitals of a complex nature, and for this purpose we started with some simple applications to atoms and to the BH molecule. 

Jacquemin, D., Champagne, B., Andre, J.-M. Molecular orbital expressions for approximate uncoupled Hartree-Fock second hyperpolarizabilities. A Pariser-Parr-Pople assessment for model polyacetylene chains. Chem. Phys. 197, 107—127 (1995)... 

More explicit molecular orbital methods including the electronic repulsion terms are called advanced molecular orbital methods. In such methods, F matrix elements of the Fock equation are calculated by Eqs. (6.6) and (6.7), and the iterative procedure, or self-consistent field (SCF) procedure must be used. The most convenient advanced molecular orbital method for the polycyclic aromatic compounds is the semiempirical method suggested by Pariser, Parr, and Pople (the PPP method). In this PPP method, the required integral values are empirically determined using the following approximations. 

---