  Transmission electron microscopy has been a promising candidate for mapping
atomic orbitals for a long time. Here, we explore its capabilities by a first
principles approach. For the example of defected graphene, exhibiting either an
isolated vacancy or a substitutional nitrogen atom, we show that three
different kinds of images are to be expected, depending on the orbital
character. To judge the feasibility of visualizing orbitals in a real
microscope, the effect of the optics aberrations is simulated. We demonstrate
that, by making use of energy-filtering, it should indeed be possible to map
atomic orbitals in a state-of-the-art transmission electron microscope.
