Charge-density waves and the displacive collective Jahn-Teller effect in alkali superoxides

The energy lowering of the observed commensurate and incommensurate charge-density-wave structures in the alkali superoxides as compared to the tetragonal structure is calculated. The charge-density waves are assumed to be driven by a collective Jahn-Teller effect associated with the orbital degeneracy of ${\mathrm{O}}_2^{-}$ ions. The results are in broad qualitative agreement with experiment, but a detailed understanding would require a more elaborate model.