Structural and electronic properties of K_nC₆₀

We present local-density pseudopotential calculations of the structural and electronic properties of potassium fulleride K_nC₆₀ (n=1,2,3,6) crystals, with an emphasis on the superconducting K₃C₆₀ phase. The calculated enthalpies of reaction for all of the potassium fullerides are within 1.4–1.7 eV per K atom. The pressure-versus-volume equation of state indicates that K₃C₆₀ is less compressible than C₆₀. The band structure K₃C₆₀ is very similar to that of C₆₀, and we discuss how it changes with pressure. Using calculated valence charge densities, we show that the valence electrons of the K atoms are almost completely transferred to the lowest unoccupied bands of the C₆₀ molecular solid.