El Khatib Muammar, Evangelisti Stefano, Leininger Thierry, Bendazzoli Gian Luigi
Laboratoire de Chimie et Physique Quantiques - LCPQ/IRSAMC, Université de Toulouse (UPS) et CNRS (UMR-5626), 118, Route de Narbonne, Toulouse Cedex, 31062, France.
J Mol Model. 2014 Jul;20(7):2284. doi: 10.1007/s00894-014-2284-7. Epub 2014 Jun 27.
Planar molecular edifices obtained by joining polyacene fragments (polyacene stripes) are investigated at tight-binding (i.e., with a Hückel Hamiltonian) and ab initio level. For this kind of system, it is known that the presence of 60-degree angles between two stripes of the polyacene molecular skeleton induces the formation of singly occupied molecular orbitals, whose combination gives rise to quasi-degenerate electronic states. In particular, two types of convex polygons having a unique side length (rhombuses and triangles) are considered in this work. It is shown that the saturation via hydrogen atoms of the apical carbons located on outer borders of the 60-degree angles increases the number of quasi-degenerate orbitals, and hence the maximal multiplicity of the low-lying states of the system. Our tight-binding and ab initio (CAS-CI, NEVPT2) calculations indicate that the spin multiplicity of these molecular structures is in systematical accord with the Ovchinnikov rule.
通过连接多并苯片段（多并苯条纹）获得的平面分子结构在紧束缚（即使用休克尔哈密顿量）和从头算水平上进行了研究。对于这类系统，已知多并苯分子骨架的两条条纹之间60度角的存在会诱导单占据分子轨道的形成，这些轨道的组合会产生准简并电子态。特别地，这项工作考虑了具有唯一边长的两种凸多边形（菱形和三角形）。结果表明，位于60度角外边界的顶端碳原子通过氢原子饱和会增加准简并轨道的数量，从而增加系统低能态的最大多重性。我们的紧束缚和从头算（CAS-CI，NEVPT2）计算表明，这些分子结构的自旋多重性与奥夫钦尼科夫规则系统地一致。
