Effect of the Wyckoff position of K atom on the crystal structure and electronic properties of KFe2Se2 compound
Abstract
By the first-principle electronic structure calculations, we study the effect of Wyckoff position of K atom on the crystal and electronic structures of KFe2Se2 compound.When the K atoms take up the Wyckoff position 2a, 2b or 4c (the related structure of KFe2Se2 is called as Struc-2a, Struc-2b or Struc-4c), the calculated lattice constant c is in the range of 13.514.5 , 15.516.7 or 18.619.1 .Three concentric cylinder-like Fermi surfaces emerge around -Z in Brillouin Zone for the Struc-2b in nonmagnetic state, different from the Struc-2a and Struc-4c.The Fe-Se-Fe angle is 107.8, 108.8 or 110.7 in the collinear anti-ferromagnetic state and the superexchange interaction J2 between two next neighbor Fe moments is 13.08 meV/S2, 20.75 meV/S2 or 11.86 meV/S2 in Struct-2a, Struc-2b or Struc-4c structure respectively.The Struc-2b and Struc-4c have a good correspondence to the newly discovered superconducting phases with Tc=40 K and Tc=30 K in KFe2Se2.Our findings provide a reasonable approach to understand the existence of multiple superconducting phases in alkali metal intercalated FeSe superconductor.
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