title: Theoretical study of the H/D isotope effect on phase transition of hydrogen-bonded organic conductor κ-H3(Cat-EDT-TTF)2.
abstract: κ-H3(Cat-EDT-TTF)2(H-TTF) is a hydrogen-bonded π-electron system which was found to reveal C2/c symmetry at 50-293 K, while its isotopologue, κ-D3(Cat-EDT-TTF)2(D-TTF), showed the phase transition at 185 K from C2/c to P1[combining macron]. To elucidate the origin of such a difference, we calculated the potential energy curves (PECs) for the hydrogen transfer along the H-bonds in these conductors. We found that both the π-stacking and the hydrogen nuclear quantum effect drastically affected the hydrogen transfer energy. By taking account of both effects, we obtained a symmetric single-well effective PEC for H-TTF, which indicated that the hydrogen was always located at the center of the H-bond. By contrast, the effective PEC of D-TTF was a low-barrier double-well, indicating that the position of the H-bonded deuterium would change according to the temperature. We concluded that the π-stacking and the nuclear quantum effect were the key factors for the appearance of phase transition only in D-TTF.
authors: Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama-City, Kanagawa, 236-0027, Japan. tachi@yokohama-cu.ac.jp.
authors: Kaichi
authors: K
authors: Yamamoto
authors: Faculty of Information Sciences, Hiroshima City University, 3-4-1, Ozuka-Higashi, Asa-Minami-Ku, Hiroshima, 731-3194, Japan.
authors: Yusuke
authors: Y
authors: Kanematsu
authors: Foundation for Computational Science (FOCUS), 7-1-28, Minatojimaminatomachi, Chuo-ku, Kobe, 650-0047, Japan.
authors: Umpei
authors: U
authors: Nagashima
authors: The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors: Akira
authors: A
authors: Ueda
authors: The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors: Hatsumi
authors: H
authors: Mori
authors: Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama-City, Kanagawa, 236-0027, Japan. tachi@yokohama-cu.ac.jp.
authors: Masanori
authors: M
authors: Tachikawa