Relaxation of zinc-blende (110) surfaces

Using the pseudofunction method and local-density theory, we have minimized the total energies of the nonpolar (110) surfaces of zinc-blende GaAs, InP, ZnTe, ZnS, HgTe, CdTe, ZnSe, CuI, CuBr, CuCl, and AgI within the framework of the rigid-rotation model of surface relaxation. Our results support the generally accepted model for GaAs and other semiconductors with low ionicity: the rigid-rotation model with a large equilibrium relaxation angle {ω}. However, we find that {ω} should decrease significantly with increasing ionicity of the semiconductor (contrary to the currently accepted viewpoint). For materials with a Phillips ionicity of about 0.74 or larger, e.g., CuBr, AgI, or CuCl, we find {ω} near zero or even negative and predict that the outward movement of the anion is nearly suppressed.