Relations between Pariser-Parr-Pople and Heisenberg models

摘要

Necessary conditions under which the lowest-energy states obtained as exact (full configuration interation) solutions of the Pariser-Parr-Pople (PPP) model may be interpreted in terms of the Heisenberg model are analyzed. In particular, for a set of model lattices the range of empirical parameters in which the lowest part of the PPP spectrum corresponds to the covalent states has been determined. It has been demonstrated that the energy gap between the lowest ionic and the highest covalent states of the PPP model, as a function of empirical parameters and of the geometric structure of the lattice, behaves in a specific and regular way. The results may be useful for determining limits of applicability of the Heisenberg model and for further studies aimed at a construction of an effective, Heisenberg-type Hamiltonian that could reproduce the lowest part of the PPP spectrum. (C) 2002 Wiley Periodicals, Inc. [References: 40]