ANGULARLY-DEPENDENT MANY-ATOM BOND ORDER POTENTIALS WITHIN TIGHT BINDING HÜCKEL THEORY
Angularly-dependent many-atom potentials for the bond order of saturated or unsaturated bonds are derived within the tight binding (TB) Hückel approximation. These potentials are firmly based on the theorem of linearized many-atom expansion for the bond order, which is novel and gives exact bond order. The explicit angular dependence appears through the moments and interference terms about a bond. Since these potentials give an appropriate description of bonding, they should play an important role in atomistic simulations for semiconductors and transition metals and their compounds. We demonstrate the rapid convergence of the many-atom series for the potentials through some illustrative examples from s bonded elements and d bonded transition metals.