Correlated electronic states of C₆₀ fragments

Abstract

We have studied electronic states of various fragments of C₆₀ within the Pariser-Parr-Pople (PPP) model and have obtained structural, magnetic and spectral properties of these molecules. The fragments studied include corannulene, fluoranthene and pyracylene. Pyracylene is studied using the exact valence bond (VB) approach while fluoranthene and corannulene are studied using a novel restricted CI technique which employs molecular orbitals for constructing the VB functions. The electronic excitations, bond order and ring currents are calculated for these systems. From these studies, the wide range of absorptions in C₆₀ can be viewed as those localized on pyracylene units or on the corannulene/ fluoranthene units. The bond orders and ring currents show the hexagons to be similar to benzene rings. The pentagon---hexagon bonds are also found to be longer than the hexagon---hexagon bonds.