Valence bond multiple excitation RVB calculations on the singlet ground states of some carbon fullerenes C-n with 20 <= n <= 60

A detailed analysis of the nature of the pi-VB Singlet ground state in term s of multiply excited resonance valence bond (RVB) wavefunctions is present ed for some carbon fullerenes in the range from 20 to 60 atoms by compariso n to exact solutions of the Heisenberg model for fullerenes of up to 30 ato ms. It is found that singlet pair excitations over an odd number of bonds a re more important than those over even ones. By far the most important cont ributions to the ground-state energies besides the non-excited Kekale RVB s pace come from those RVB functions containing singlet pair excitations over three carbon bonds. (C) 1998 Elsevier Science B.V. All rights reserved.