Ratio between the largest and smallest moment of inertia (I_z/I_x) with respect to the ratio between the intermediate moment of inertia to the smallest one (I_y /I_x) for three selected sets of nanoclusters. The black circle indicates the ratio that defines a perfect sphere (I_y /I_x = I_z /I_x = 1), while the dashed lines show the prolate (I_z = I_y > I_x) and oblate (I_x = I_y < I_z) limits. (A) Lowest energy O-N and P-N nanoclustersfor N = 1–10 and SiO-N nanoclustersfor N = 1–20, grey area corresponds to the plotted area in (B). (B) Zoom of the plot in (A) over a 1.0–1.8 range for both axes. (C) 180 P-6 nanocluster isomers. (D) 180 O-6 nanocluster isomers.