In detail, density-functional theory (DFT) calculations are performed using the Vienna ab initio simulation package (VASP) . The generalized gradient approximation (GGA) with the PBE functional is used to model the electron exchange and correlation interaction. The electron-ion interaction is described by the projectoraugmented wave (PAW) scheme . The electronic wave functions are expanded into plane waves up to a kinetic energy cutoff of 400 eV. The Brillouin zone integration is performed using Γ-centered 4 × 4 × 1 meshes. The (001) surfaces are modeled by supercells containing 13 and 14 atomic layers for cation and anion terminated surfaces, respectively, and a vacuum region of ∼13.5 Å. The slab bottom dangling bonds are saturated with fractionally charged H atoms. The electric field resulting from the inequivalence of the two surfaces is taken into account by a dipole correction to the electrostatic potential. The atoms are structurally relaxed until they experience forces smaller than 0.02 eV/ Å. The calculations are performed at the equilibrium lattice parameter of Al 0.5 In 0.5 P calculated to be 5.751 Å.