Structure and energy related properties of neutral and charged vacancies on relaxed diamond (100) (2x1) surface were investigated by means of density functional theory. Calculations indicate that the diffusion of a single vacancy from the top surface layer to the second layer is not energetically favored. Analysis of energies in charged system shows that neutral state is most stable on diamond (100) (2x1) surface. The multiplicity of possible states can exist on diamond (100) surface in dependence on the surface Fermi level, which supports that surface diffusion of a vacancy is mediated by the change of vacancy charge states. Analysis of density of states shows surface vacancy can be effectively measured by photoelectricity technology. Crown Copyright (C) 2008 Published by Elsevier B. V. All rights reserved.