Monkhorst-Pack 30 meshes of k-points with a spacing of 0.07 2π Å -1 was used with plane-wave cutoff energy of 340 eV. The on-the-fly generated (OTFG) ultrasoft pseudopotentials QC5 were used. A subset of structures was then reoptimized using harder OTFG C19 pseudopotentials and with tighter convergence settings (700 eV energy cutoff and Monkhorst-Pack k-point spacing of 0.05 2π Å -1 ) to refine the structures and their energetics (i.e. refined search).