Electronic Structure and Charge Transfer in the κ - BEDT-TTF₂Cu₂( CN)₃ Organic Conductor: The Role of Cu²⁺ Impurities
Kuzmin A.V., Khasanova E.I., Khasanov S.S.

Received: December 17, 2025

DOI: 10.7868/S3034641X26030055

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The single crystals of the layered organic conductor κ - BEDT-TTF₂ Cu₂( CN)₃ were studied by X-ray diffraction and X-ray photoemission spectroscopy. The electronic structure of the conducting BEDT-TTF₂ layer and its Fermi surface details were analyzed by quantum chemical calculations within the DFT level theory based on structure model of the isolated positively charged conducting layers in a virtual charge compensation medium. Although the accepted stoichiometry for the κ -salts corresponds to the half-filled band structure model with a charge transfer level of q = 0.5 for the dimers \left [ BEDT-TTF₂\right ]^2q+, it was found that, for the crystals studied, minimum of the corrections to the system's total energy reaches a minimum at q = 0.488. This theoretically found charge reduction in the cationic conducting layer is presumably associated with the presence of positively charged impurities within the anion layer. Indeed, X-ray photoemission spectroscopy measurements taken in this work clearly show the presence of Cu²⁺ impurities, which reduce the average negative charge of the anion layer and, consequently, the positive charge of the layer of cationic conducting dimers. The consequences of this result for the conducting properties of the crystal are also discussed. Keywords:} organic conductors, crystal structure, low temperatures, DFT