First-Principles Study of Hydrogen Bonded Molecular Conductor κ-H3(Cat-EDT-TTF/ST)2; Electronic Structure and Role of the Hydrogen Bonds
Proton dynamics in relatively short intermolecular hydrogen bonds play an essential role in various functional molecular materials such as organic ferroelectrics and biochemical reactions. Recently, a new class of hydrogen bonded molecular conductors has been synthesized; the compounds are based on catechol with ethylenedithiote-tetrathiafulvalene, Cat-EDT-TTF and its diselena analog Cat-EDT-ST. Among them, κ-type H3(Cat-EDT-TTF)2 is considered to be a dimer-type Mott insulator at ambient pressure and emerges as a candidate of realizing quantum spin liquid down to lowest temperature . In this crystal, two H(Cat-EDT-TTF) units share a hydrogen (H) atom with relatively short O-H-O hydrogen bonds, and its face-to-face dimers are formed in an anisotropic triangular lattice.
We study the electronic and structural properties of κ-H3(Cat-EDT-TTF/ST)2 by first-principles density functional theory (DFT) calculations . We report unique properties of electronic structure compared with conventional molecular conductors. To discuss a possibility of spin-frustration, we evaluate inter-dimer transfer integrals by fitting the DFT band structure. Regarding the hydrogen bonds, we calculate the potential energy surface to investigate the degree of localization of the shared H atom and discuss the stability of the structures. Lastly, we discuss how the positions of the shared H atom influence to the electronic properties.
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