  During the last few years, it has become more and more clear that functionals
of the meta generalized gradient approximation (MGGA) are more accurate than
GGA functionals for the geometry and energetics of electronic systems. However,
MGGA functionals are also potentially more interesting for the electronic
structure, in particular when the potential is non-multiplicative (i.e., when
MGGAs are implemented in the generalized Kohn-Sham framework), which may help
to get more accurate bandgaps. Here, we show that the calculation of bandgap of
solids with MGGA functionals can be done very accurately also in a
non-self-consistent manner. This scheme uses only the total energy and can,
therefore, be very useful when the self-consistent implementation of a
particular MGGA functional is not available. Since self-consistent MGGA
calculations may be difficult to converge, the non-self-consistent scheme may
also help to speed-up the calculations. Furthermore, it can be applied to any
other types of functionals, for which the implementation of the corresponding
potential is not trivial.
