SYMMETRIZED PROJECTOR QUANTUM MONTE-CARLO STUDIES OF THE GROUND-STATEOF C-60

We develop a symmetrized version oi the projector quantum Monte Carlo (SPQMC) method which preserves the symmetries of the system by simulta neously sampling all symmetry-related Ising configurations at each MC step and use it tu study the effect of electron correlations on a sing le C-60 molecule and its structural motifs, within the Hubbard model, This SPQMC method allows more accurate estimates of correlation functi ons as seen from calculations on small systems. The method applied to some molecular fragments of C-60 viz., pyracylene, fluoranthene, and c orannulene, gives a good chemical description of these systems, Analys is of the ground-state bond orders allows us rc, visualize pyracylene as a naphthalene moiety with weakly bridged ethylenic units, fluoranth ene as weakly bridged naphthalene and benzene units, and corannulene a s radialene with ethylenic bridges. We study the ground-state properti es of a single fullerene molecule, with and without bond alternation. Tile bond orders in the ground state for the two types of nearest-neig hbor bonds are unequal, even for uniform C-60. The spin and charge cor relations give a consistent picture of the interacting ground state in all these systems. We construct projections of the bond orders and sp in-spin correlation functions on the space of irreducible representati ons of the icosahedral point group. These projections, analogous to th e structure factors of translationally invariant systems, give the amp litudes for distortions which transform as the irreducible representat ions or the point group. The amplitude for the H-g distortion is the l argest, while the spin structure has large weights in the T-2g and G(u ) representations.