  Although topological surface states are known to be robust against
non-magnetic surface perturbations, their band dispersions and spatial
distributions are still sensitive to the surface defects. Take Bi2Se3 as an
example, we demonstrated that Se vacancies modifies the surface band structures
considerably. When large numbers of Se vacancies exist on the surface,
topological surface states may sink down from the first to second quintuple
layer and get separated from the vacancies. We simulated STM images to
distinguish the surfaces with Se- and Bi-terminations.
