First-Principles Study of Hydrogen Bonded Molecular Conductor -H3(Cat-EDT-TTF/ST)2; Electronic Structure and Role of the Hydrogen Bonds

Takao Tsumuraya 

ICYS-Namiki researcher

 

 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, -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 [1]. 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 -H3(Cat-EDT-TTF/ST)2 by first-principles density functional theory (DFT) calculations [2]. 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.

 

[1] T. Isono, H. Kamo, A. Ueda, K. Takahashi, M. Kimata, H. Tajima, S. Tsuchiya, T. Terashima, S. Uji, and H. Mori, Phys. Rev. Lett. 112, 177201 (2014), and references therein.

[2] T. Tsumuraya, H. Seo, R. Kato and T. Miyazaki, Phys. Rev. B 92, 035102 (2015).