  The band structures of bulk transition metal dichalcogenides ReS2 and ReSe2
are presented, showing the complicated nature of the interband transitions in
these materials, with several close-lying band gaps. Three-dimensional plots of
constant energy surfaces in the Brillouin zone at energies near the band
extrema are used to show that the valence band maximum and conduction band
minimum may not be located at special high symmetry points. We find that both
materials are indirect gap materials and that one must be careful to consider
the whole Brillouin zone volume in addressing this question.

Mesoscale and Nanoscale Physics