DFT calculations of crystalline structures were performed using the GPAW simulation package of the Atomic Simulation Environment. The GPAW package is a real space grid algorithm based on the projector-augmented wavefunction method amond, respectively. DFT calculations were performed using the PBE (Perdew-Burke-Ernzerhof) exchange-correlation functional with a kinetic energy cutoff of 600 eV and the Brillouin zone integration was done with Monkhorst-Pack grids with a density of 2.5 k points per Å -1 .