  The modified Becke-Johnson exchange potential combined with local-density
approximation correlation (mBJLDA) has recently attracted interest because it
provides highly improved band gaps at a very low computational cost. In this
work we performed an extensive investigation of the performance of the mBJLDA
potential employing a norm-conserving pseudopotential plane-waves approach
(mBJLDA@PP), as implemented in the abinit code, using a test set of 83 solids
representing a wide range of semiconductors and insulators. Our results confirm
the conclusion of our previous study that the number of electrons treated as
valence in the pseudopotentials of the cations can have a significant impact on
the calculated mBJLDA@PP band gaps. More specifically, while the use of typical
pseudopotentials leads to accurate band gaps of certain systems, it yields
significantly underestimated band gaps for other systems compared to experiment
and to those of the all-electron mBJLDA (mBJLDA@AE) approach. The classes of
the latter systems are identified, and this problem is resolved by including
some outer core states as valence. The resulting mean absolute error in the
calculated band gaps (compared to experiment) is of 0.46 eV, which is
comparable to that of the mBJLDA@AE band gaps, reflecting the accuracy and
reliability of the mBJLDA@PP approach for the band gap calculations.
