Structural, electronic, magnetic and elastic properties of tetragonal layered diselenide KCo2Se2 from first principles calculations

The structural, elastic, magnetic and electronic properties of the layered tetragonal phase KCo2Se2 have been examined in details by means of the first-principles calculations and analyzed in comparison with the isostructural KFe2Se2 as the parent phase for the newest group of ternary superconducting iron-chalcogenide materials. Our data show that KCo2Se2 should be characterized as a quasi-two-dimensional ferromagnetic metal with highly anisotropic inter-atomic bonding owing to mixed ionic, covalent, and metallic contributions inside [Co2Se2] blocks, and with ionic bonding between the adjacent [Co2Se2] blocks and K sheets. This material should behave in a brittle manner, adopt enhanced elastic anisotropy rather in compressibility than in shear, and should show very low hardness.