Fig. 9. Lattice energy versus density plot for all low energy structures found in the present study. The structures are all optimized at the vdW-DF2 level with energies calculated with (a) vdW-DF2 functional implemented in Quantum ESPRESSO; (b) PBE+TS method in FHI-aims; (c) the PBE+MBD method in FHI-aims. I – black square, II – red circle, III – green up triangle, IV – blue down triangle, V – dark yellow diamond. The polytypic structures of I and II are marked with open symbols of the same colors and shapes. All experimental structures have energies within the range highlighted by the horizontal dashed line.