Low-energy structures of K atoms in expanded K₃C₆₀ monolayers: Ab initio pseudopotential density-functional calculations

We have performed ab initio pseudopotential density-functional calculations to study spatial distributions of potassium atoms in expanded K₃C₆₀ monolayers and their effects on the conduction bands from the C₆₀’s lowest unoccupied molecular orbitals (LUMOs). Our results show that, as the lattice constant a of the monolayer increases, the lowest-energy configuration for the potassium atoms changes from a honeycomb (a<10.8 Å) to a kagome lattice (a>11.4 Å), with an intermediate phase appearing in between. The calculated electronic structures show that the C₆₀-LUMO-derived conduction bands are deformed sensitively by the presence and location of the dopants in the intermediate and the kagome-lattice phases, deviating greatly from the rigid-band picture. The sensitivity to the dopants may provide a method for tailoring the C₆₀-derived electronic structures.