All periodic calculations were performed using the VASP software in versions 5.4 and 6.2. Tests showed no differences in energies and forces between the two versions; therefore the upgrade to version 6.2 was made during the project to benefit from recent performance improvements. PAW PBE pseudopotentials of version 5.4 were used. The PBE functional was used in conjunction with the D3BJ dispersion correction method at an energy cutoff value of Gcut = 800 eV to perform spin unrestricted calculations in the Γ-only approximation. The electronic convergence criterion was set to 10 -8 eV, and a Gaussian smearing of width 0.01 eV was applied to the orbital occupations. An "accurate" grid (meaning 2*Gcut FFT-grid points along every cell vector) was used. Geometry optimizations and nudged elastic band (NEB) calculations employed a force convergence criterion of 0.02 eV/Å. Single point (SP) energy calculations were performed using the range-separated hybrid functional HSE06, also using D3BJ dispersion correction and the same settings as described above.