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Advancing adsorption on an n-type InSb(110) surface induces gradual formation of a carrier-depletion layer at the surface. Incorporating a highly nonparabolic (NP) dispersion of the conduction band into the local-density-functional formalism in a complete manner, we investigate evolution of electron states at the n-type InSb surface in the depletion-layer formation process. By comparing the calculated results for the NP dispersion with those for the parabolic (P) dispersion corresponding to the band-edge effective mass, we evaluate the effects of the nonparabolicity on surface electron states. The nonparabolicity is found to make significant differences in the effective one-electron potential and the carrier-density distribution at the surface. The band bending occurs in the closer vicinity of the surface and with a smaller bending magnitude in the NP dispersion than in the P dispersion. This can be explained by the fact that carrier electrons operate to screen positive charges of ionized donors in the depletion layer more effectively in the NP dispersion than in the P dispersion. Accurate treatment of the nonparabolicity is indispensable in evaluating the surface electron states at each stage of the formation process.

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