A new format for describing the interactions among atoms capable of covalent bond formation is introduced and applied to sulfur in both molecular cluster and bulk amorphous forms. Bonding is described locally and evaluated via a semi-empirical quantum-chemical expression, while non-bonding interactions are described by conventional molecular mechanics. The new method is shown to capture the essential features of both the molecular and bulk phases in a generalizable format with few adjustable parameters, while retaining the computational efficiency required for the simulation of bulk condensed phase systems.