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

The accuracy of the analytic bond-order potentials (BOP's) that were derive d in the previous paper within the tight-binding (TB) formalism is studied for the case of diamond, graphite, and the hydrocarbon molecules. The simpl ified four-level variant, BOP4S, is found to reproduce the TB bond orders o f the C-I-I and C-C sigma bonds to better than 6% due partly to the inclusi on of the shape parameter (b(2)/b(1))(2). The two-level matrix-derived expr ession BOP2M is shown to provide a good description of the saturated and co njugate pi bonds, thereby overcoming the deficiencies of the Tersoff potent ial that are associated with overbinding of radicals and poor treatment of conjugacy. The analytic BOP's reproduce the C-II and C-C bond energies to b etter than 0.9 eV per bond. The errors would be reduced if the analytic pot entials were fitted to experiment rather than predicted directly from known TB parameters. [S0163-1829(99)02813-1].