Kato Takashi, Yamabe Tokio
Institute for Innovative Science and Technology, Graduate School of Engineering, Nagasaki Institute of Applied Science, 3-1, Shuku-machi, Nagasaki 851-0121, Japan.
J Phys Chem B. 2005 Jun 2;109(21):10620-30. doi: 10.1021/jp0406823.
Electron-phonon interactions in the monoanions of polyacetylenes such as C2H4 (2tpa), C4H6 (4tpa), C6H8 (6tpa), and C8H10 (8tpa) are studied and compared with those in the monoanions of polyacenes. The C-C stretching A(g) modes around 1500 cm(-1) the most strongly couple to the lowest unoccupied molecular orbitals (LUMO) in polyacetylenes. The estimated total electron-phonon coupling constants for the monoanions (l(LUMO)) are 0.579, 0.555, 0.463, and 0.401 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. The l(LUMO) values for polyacetylenes are much larger than those for polyacenes. Furthermore, the l(LUMO) value for polyacetylene with C(2h) geometry is estimated to be 0.254 eV, and is larger than that (0.024 eV) for polyacene with D(2h) geometry. The phase patterns difference between the LUMO of polyacenes localized on the edge part of carbon atoms, and the delocalized LUMO of polyacetylenes is the main reason for the calculated results. The single charge transfer through the molecule in polyacetylenes are also discussed. The reorganization energies between the neutral molecule and the corresponding monoanion are estimated to be 0.164, 0.144, 0.125, and 0.113 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. Such reorganization energy decreases with an increase in molecular size. The conditions under which the attractive electron-electron interactions are realized in the monoanions of polyacetylenes and polyacenes are discussed. In terms of the electron-phonon interactions and the reorganization energies, the relationships between the normal and possible superconducting states are briefly discussed. We find that the monoanions with smaller molecular size cannot easily become good conductors, however, the conditions under which the interactions between two electrons are attractive are more easily realized in the monoanions with smaller molecular size than in the monoanions with larger molecular size.
研究了聚乙炔单阴离子（如C2H4（2tpa）、C4H6（4tpa）、C6H8（6tpa）和C8H10（8tpa））中的电子-声子相互作用，并与并苯单阴离子中的相互作用进行了比较。聚乙炔中1500 cm(-1)附近的C-C伸缩A(g)模式与最低未占据分子轨道（LUMO）耦合最强。对于2tpa、4tpa、6tpa和8tpa，单阴离子的估计总电子-声子耦合常数（l(LUMO)）分别为0.579、0.555、0.463和0.401 eV。聚乙炔的l(LUMO)值远大于并苯的l(LUMO)值。此外，具有C(2h)几何结构的聚乙炔的l(LUMO)值估计为0.254 eV，大于具有D(2h)几何结构的并苯的l(LUMO)值（0.024 eV）。并苯LUMO定域在碳原子边缘部分，与聚乙炔离域LUMO之间的相位模式差异是计算结果的主要原因。还讨论了聚乙炔中通过分子的单电荷转移。对于2tpa、4tpa、6tpa和并苯，中性分子与相应单阴离子之间的重组能估计分别为0.164、0.144、0.125和0.113 eV。这种重组能随分子尺寸的增加而降低。讨论了在聚乙炔和并苯单阴离子中实现吸引性电子-电子相互作用的条件。根据电子-声子相互作用和重组能，简要讨论了正常态和可能的超导态之间的关系。我们发现，分子尺寸较小的单阴离子不容易成为良导体，然而，与分子尺寸较大的单阴离子相比，分子尺寸较小的单阴离子更容易实现两个电子之间的吸引性相互作用的条件。
