  We investigate the bulk band structures and the surface states of Bi2Se3 and
Bi2Te3 topological insulators using first-principles many-body perturbation
theory based on the GW approximation. The quasiparticle self-energy corrections
introduce significant changes to the bulk band structures, while their effect
on the band gaps is opposite in the band-inversion regime compared to the usual
situation without band inversion. Parametrized "scissors operators" derived
from the bulk studies are then used to investigate the electronic structure of
slab models which exhibit topologically protected surface states. The results
including self-energy corrections reveal significant shifts of the Dirac points
relative to the bulk bands and large gap openings resulting from the
interactions between the surface states across the thin slab, both in agreement
with experimental data.
