An analytic interatomic bond-order potential BOP is derived that depends explicitly on the group number of the sp -valent element. This is achieved by generalizing the previously published BOP for group-IV elements by extrapolating from half-full occupancy using a simple envelope function for the upper bound of the bond order. This interatomic potential predicts the structural trends across the sp -valent elements that are found by our tight-binding reference calculations and observed by experiment. Unlike empirical interatomic potentials this theoretically derived BOP includes the valence-dependent character of the bonding naturally within its remit.
