Ultrasoft pseudopotentials with kinetic energy density support: implementing the modified Becke-Johnson potential

We extend the Vanderbilt ultrasoft pseudopotential scheme by adding kinetic energy density terms, in order to use meta-GGA exchange potentials, such as the Becke-Johnson or Tran-Blaha potentials, in the planewave-pseudopotential implementation of Density Functional Theory. Having implemented kinetic energy augmentation and non-linear core correction terms in the CASTEP density functional package, we evaluate the validity of our approach by comparing the calculated electronic structure of isolated atoms and semiconductor crystals to all-electron benchmark calculations. Based on our results, we provide recommendations for the practical use of the Tran-Blaha exchange in planewave-pseudopotential codes.