Caetano E W S, Freire V N, Dos Santos S G, Galvão D S, Sato F
Centro Federal de Educação Tecnológica do Ceará, Avenida 13 de Maio, 2081, Benfica, 60040-531 Fortaleza, Ceará, Brazil.
J Chem Phys. 2008 Apr 28;128(16):164719. doi: 10.1063/1.2908739.
Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists N(t) varying from 0 to 7 (the case N(t)=1 corresponds to a half-twist Möbius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO-->LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.
本文给出了扭转数(N(t))从(0)到(7)的扭转石墨烯纳米带的经典力场几何优化结果（(N(t)=1)的情况对应于半扭转莫比乌斯纳米带）。使用布伦纳反应力场研究了它们的结构稳定性。最佳的经典分子几何结构用作半经验计算的输入，从中计算出每种结构的电子性质（能级、最高占据分子轨道、最低未占分子轨道）。还在完全活性空间框架内计算了组态相互作用波函数，考虑了从最高占据分子轨道(-4)到最低未占分子轨道(+4)的本征态，以及对应于紫外-可见范围内首次光学跃迁的振子强度。发现能量最低的分子比初始构型对称性更低，并且由于扭转产生的电子局域化效应，最高占据分子轨道-最低未占分子轨道能隙大于用于构建它们的纳米石墨烯的能隙值。大量扭转导致最高占据分子轨道向最低未占分子轨道跃迁能量急剧增加。我们认为一些扭转纳米带可以形成由偶极相互作用稳定的晶体。
