Temperature-concentration phase diagram of P2-NaxCoO2 from first-principles calculations
نویسندگان
چکیده
Temperature-concentration phase diagrams for NaxCoO2 "0.5!x!1! are obtained by combining density functional theory "DFT! in the generalized gradient approximation "GGA! and in the GGA with Hubbard U correction "GGA+U! with the cluster expansion and Monte Carlo simulation technique. In the GGA, holes are delocalized over the Co layer, while in GGA+U the charges on the Co layer completely localize, forming distinct Co3+ and Co4+ cations. The leading interactions in GGA are long-range in-plane electrostatics and relaxation effects, whereas in GGA+U Co-Co interactions dominate. Comparison of ground states, c-lattice parameter, and Na1/Na2 ratio with experimental results consistently suggests that GGA is a better approximation for 0.5!x!0.8.
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