Effect of cation deficiency on the electronic properties and on the Fermi surface topology of K1−xNi2−ySe2 from first principles calculations

Soon after the discovery of superconductivity in layered Fe-Ch systems, the intense search of related Fe-free materials has been begun. It was found that these systems such as KxNi2(S,Se)2 are cation-deficient, and the superconducting state should be sensitive to the presence of K and Ni vacancies. Herein, using the first principles FLAPW-GGA calculations, we have studied the electronic structure and Fermi surface (FS) topology for cation-deficient K1−xNi2−ySe2. We have found that the presence of potassium vacancies (for K0.8Ni2Se2) as well as the joint effect of K and Ni vacancies (for K0.8Ni1.6Se2) change essentially the topology of their FSs and the character of electronic bands. Unlike 2D-like FS for stoichiometric KNi2Se2, the FSs for cation-deficient compositions demonstrate much more complex topology of mixed 2D-3D type.