Derivation and Analysis of the Pariser–Parr–Pople Model

Second quantization formalism is used to derive the Pariser–Parr–Pople model for planar unsaturated molecules. The model is analyzed in detail in the atomic limit and the equivalence with an Heisenberg antiferromagnet is demonstrated by perturbation theory. An approximate Green's-function method is developed and its properties in the same limit are derived and shown to be correct. The case of a linear chain is calculated explicitly and compared with other results. Limitations and difficulties in the establishment of the results are discussed.