Collect. Czech. Chem. Commun. 1988, 53, 1910-1918

The application of inner projection technique to many electron systems as compared with the coupled cluster expansion. A study of the Pariser-Parr-Pople model of the benzene molecule

Jiří Čížeka,b,c and Francine Vinettec

a Guelph-Waterloo Center for Graduate Work in Chemistry, University of Guelph and University of Waterloo
b Laboratoire de photophysique moléculaire du CNRS, Bâtiment 213 – Université de Paris-Sud, 91405 Orsay Cédex, France
c University of Waterloo, Waterloo, Ontario, Canada N2L 3G1


The technique of inner projection is used for the first time in a chemical context, namely for the study of the ground state energy of the Pariser-Parr-Pople model of the benzene molecule. The lower bound for the energy is calculated for three types of parametrization. These results are compared with the “exact” energies which are obtained from full configuration interaction. It is shown that the inner projection technique provides very good lower bounds for the energy. In addition, we compare these inner projection results with those obtained by other approximative techniques, namely with the results of the Coupled Pair Many Electron Theory. A discussion of the application of the method of intermediate hamiltonians and the inner projection technique is also included.