The most stable geometry for each concentration of sodium is shown in Figure and Adding another sodium atom into the conventional unit cell, the concentration Na 0.5 FeHCF is reached. The sodium atoms are arranged in a diagonal stack within a yz-plane, leading to alternating layers of empty and diagonally stacked yz-planes throughout the crystal. This would, of course, also apply to any symmetry-equivalent structures, where other planes are stacked on top of each other. The results published by Wang et al. align with this finding.