Trends in structural, electronic properties and Fermi surface topology of 15 tetragonal ThCr2Si2-type phases AFe2Ch2, where A = Li, Na, K, Rb, and Cs; Ch = S, Se, and Te, as parent systems of new ternary iron–chalcogenide superconducto

By means of the first principles FLAPW-GGA approach, a systematic study of the structural and electronic properties of full series of 15 synthesized and hypothetical tetragonal ThCr2Si2-type phases in the system A–Fe–Ch, where A = Li, Na, K, Rb, and Cs; Ch = S, Se, and Te, was performed. We find that for the tuning of the structural parameters of conducting [Fe2Ch2] blocks the replacements of Ch2− ions will be most effective, whereas for the tuning of the inter-blocks separation [Fe2Ch2]–[Fe2Ch2] the replacements of the alkaline ions seem more useful. The trends in the electronic properties and Fermi surface topology of AFe2Ch2 phases are analyzed in relation to their structural parameters to explore whether these materials can be as the parent systems for new ternary iron–chalcogenide superconductors. For all these systems, similar multi-sheet Fermi surfaces consist exclusively of electronic-like sheets, two of which are 2D-like sheets in the corners of the Brillouin zone, and the third one is a closed pocket around Z. The total DOSs at the Fermi level are related with the type of anion Ch2− and their values grow in the sequence AFe2S2 → AFe2Se2 → AFe2Te2. Thus we assume that AFe2Se2 and AFe2Te2 phases may be considered as favorable parent systems for the search of new ternary iron–chalcogenide SCs.