Doping effects on the electronic and structural properties of CoO2:: An LSDA+U study -: art. no. 085108

A systematic local spin density approximation (LSDA)+U study of doping effects on the electronic and structural properties of single layer CoO2 is presented. Undoped CoO2 is a charge transfer insulator within LSDA+U and a metal with a high density of states (DOS) at the Fermi level within LSDA. (CoO2)(1.0-), on the other hand, is a band insulator with a gap of 2.2 eV. Systems with fractional doping are metals if no charge orderings are present. Due to the strong interaction between the doped electron and other correlated Co d electrons, the calculated electronic structure of (CoO2)(x-) depends sensitively on the doping level x. Zone center optical phonon energies are calculated under the frozen phonon approximation and are in good agreement with measured values. Softening of the E-g phonon at doping xsimilar to0.25 seems to indicate a strong electron-phonon coupling in this system. Possible intermediate spin states of Co ions, Na ordering, as well as magnetic and charge orderings in this system are also discussed.