The KSC unit cell contains 36 atoms and was used for all DFT calculations. As the widely used exchange-correlation functional suggested by Perdew, Burke, and Ernzerhof results in a lattice constant of 10.25 Å which is far above the experimental value of 10.01 Å, in addition, the PBEsol functional and the SCAN functional were tested. The resulting values for the lattice constant, 9.97 Å and 9.96 Å respectively, agree far better with the experimental result. Consequently, the PBEsol functional was used for most of the geometry optimizations and the more computationally expensive SCAN meta-generalized gradient approximation, which is known to yield significantly improved formation energies compared to generalized gradient approximation-based functionals, was used for certain samples only. The density of states was determined by employing the HSE06 functional. The ionic cores were treated with the projector augmented wave method, as implemented in the Vienna Ab Initio Simulation Package. Electronic wave functions were expanded up to energies of 600 eV and it was made sure that total energies converged within a few meV/atom concerning the number of kpoints in the first Brillouin zone. All structures were optimized until the entries of the stress tensor and all forces were below 0.01 eV/Å without constraining any internal degree of freedom.