Analytic bond-order potentials beyond Tersoff-Brenner. II. Application to the hydrocarbons

The accuracy of the analytic bond-order potentials ~BOP’s! that were derived in the previous paper within the tight-binding ~TB! formalism is studied for the case of diamond, graphite, and the hydrocarbon molecules. The simplified four-level variant, BOP4S, is found to reproduce the TB bond orders of the C-H and C-C s bonds to better than 6% due partly to the inclusion of the shape parameter (b2 /b1) . The two-level matrixderived expression BOP2M is shown to provide a good description of the saturated and conjugate p bonds, thereby overcoming the deficiencies of the Tersoff potential that are associated with overbinding of radicals and poor treatment of conjugacy. The analytic BOP’s reproduce the C-H and C-C bond energies to better than 0.9 eV per bond. The errors would be reduced if the analytic potentials were fitted to experiment rather than predicted directly from known TB parameters. @S0163-1829~99!02813-1#