The Magnetic Suppression and Electronic Structure Evolution of K 1- x Fe 2 Se 2 with Different K Vacancy Concentration

Magnetic and electronic structures of K 1- x Fe 2 Se 2 ( x = 0.0, 0.2, 0.4, 0.6, and 0.8) in collinear antiferromagnetic state were studied by first-principles calculations. With the increase of K vacancy concentration, the magnetic moment and Fe-Se bond length were decreased (from x = 0.0 to 0.6) first and then increased (from x = 0.6 to 0.8). When the K vacancy concentration was 0.6 (that is K 0.4 Fe 2 Se 2 ), the magnetic moment was completely suppressed, and the Fe-Se bond was the smallest. In contrast, the hybridized band width (HBW) first increased and then decreased, reaching to the maximum for K 0.4 Fe 2 Se 2 . The electron Fermi surface shrank gradually and the hole Fermi surface grew. The calculated results explained why experimental K 0.8 Fe 2 Se 2 showed superconductivity compared with KFe 2 Se 2 .