The study of the strength of correlations in NaxβCoO2β is extended to the
x=0 end of the phase diagram where Mott insulating behavior has been widely
anticipated. Inclusion of correlation as modeled by the LDA+U approach leads to
a Mott transition in the agβ subband if U is no less than Ucβ=2.5 eV. Thus
U smaller than Ucβ is required to model the metallic, nonmagnetic CoO2β
compound reported by Tarascon and coworkers. The orbital-selective Mott
transition of the agβ state, which is essentially degenerate with the
egβ²β states, occurs because of the slightly wider bandwidth of the agβ
bands. The metal-insulator transition is found to be strongly coupled to the
Co-O bond length, due to associated changes in the t2gβ bandwidth, but the
largest effects occur only at a reduced oxygen height that lies below the
equilibrium position.Comment: 8 pages with 9 embedded figure