Role of elastic interaction in the disordered-pyrite to ordered-pyrite phase transition in sodium superoxide

We analyze the effect of indirect orientation-dependent elastic coupling between molecules, recently studied by Michel and Naudts in NaCN and KCN, on the disordered-pyrite to ordered-pyrite phase transition in sodium superoxide (Na${\mathrm{O}}_2$). We find that the inclusion of this indirect interaction does not affect our earlier results on the order-disorder transition obtained by including only the direct interaction between the ${\mathrm{O}}_2^{-}$ molecules. We also discuss the interplay between direct and indirect interaction in the structural phase transitions seen in other alkali superoxides.