of in-plane strain anisotropy in ZnSe(001)/GaAs layers using reflectance difference spectroscopy J.We investigated the possibility that the interface energy in heteroepitaxial compound semiconductor systems can be characterized by a unique value. We suggest that the per-bond binding energy, which is associated with the strength of the chemical bonds that span the interface between the different compounds, is this desired value. We chose the ZnSe͑001͒/GaAs͑001͒ system for this study because of its relatively small lattice mismatch. Three chemically different interfaces were studied: One containing only Ga-Se bonds, one containing only Zn-As bonds, and one with an equal ͓i.e., 50:50͔ mixture of these bonds. We employed first-principles density-functional theory electronic-structure calculations to obtain the structure and binding energy of the bonds and these interfaces, for a variety of unit cells in order to find the favored configurations under static lattice conditions. The destabilizing effect of an interfacial charge imbalance, and, one of the limitations of density-functional theory calculations in this circumstance are also discussed.