Effects of local oxygen distortions on the electronic structure of NaxCoO2 -: art. no. 214503

By using the pseudopotential method with the local spin-density functional approximation, the electronic band structure of NaxCoO2 is calculated for x=0.25, 0.5, 0.75, and x=1 in the presence of the structure relaxations. As the Na content increases, a phase transition is predicted from a wide-band ferromagnetic to a narrow-band paramagnetic metal. The itinerant ferromagnetism is strongly suppressed by the local distortions of the oxygens around the cobalts. Moreover, straining the CoO2 layers corresponding to the hydrated superconductor Na0.35CoO2.1.3H(2)O strongly enhances the ferromagnetism.