Identifying hydrogen atoms on graphite

We comment on the identification of a hydrogen atom adsorbed on graphite and distinguishing it from closely-spaced pairs under the scanning tunneling microscope (STM) through electronic state calculations based on density functional theory. The presence of the H atom should be very well observable through a distinct feature most directly associated with the adsorbate itself, a threefold symmetry most apparent through the third-nearest neighbor C atoms, and through sublattice visibility differences. A comparison with effects on the electronic states brought about by closely-spaced pairs shows visible differences in the aforementioned three factors, which should enable us to discriminate among adsorbed structures. Results compare well with STM measurements of adsorbed deuterium on graphite.