  Following the discovery of the potentially very high temperature
superconductivity in monolayer FeSe we investigate the doping effect of Se
vacancies in these materials. We find that Se vacancies pull a vacancy centered
orbital below the Fermi energy that absorbs most of the doped electrons.
Furthermore we find that the disorder induced broadening causes an effective
hole doping. The surprising net result is that in terms of the band structure
Se vacancies behave like hole dopants rather than electron dopants. Our results
exclude Se vacancies as the origin of the large electron pockets measured by
angle resolved photoemission spectroscopy.
