Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah 711103, India.
Chemphyschem. 2011 Oct 24;12(15):2791-7. doi: 10.1002/cphc.201100430. Epub 2011 Aug 26.
We present improved virtual orbital (IVO) complete active space (CAS) configuration interaction (IVO-CASCI) and IVO-CASCI-based multireference Møller-Plesset perturbation theory (MRMPPT) calculations with an aim to elucidate the electronic structure of tetramethyleneethane (TME) in its lowest singlet and triplet state and to quantify their order and extent of splitting. The potential surfaces of singlet and triplet states for the twisting of TME are also studied. We found that the triplet state is higher in energy than the singlet one in the whole range of twisting angles with the energy gap minimum at a twisting angle of about 45°. Harmonic vibrational frequencies of TME have also been calculated for both the states. We also report the ground to first excited triplet state transition energies. Our results are analyzed with respect to the results available in the literature to illustrate the efficacy of our methods employed. We also demonstrate that the spin character of the ground state of disjoint, TME-like diradicals can be manipulated by using appropriate selection of annulenic spacer to separate the allyl groups of TME.
我们提出了改进的虚轨道（IVO）完全活性空间（CAS）组态相互作用（IVO-CASCI）和基于IVO-CASCI 的多参考Møller-Plesset 微扰理论（MRMPPT）计算，旨在阐明四亚甲基乙烷（TME）在其最低 singlet 和 triplet 态的电子结构，并量化它们的分裂顺序和程度。还研究了 TME 扭曲的 singlet 和 triplet 态的势能面。我们发现，在整个扭曲角度范围内，三重态的能量都高于单重态，在扭曲角度约为 45°时能量差最小。还计算了两种状态下 TME 的谐波振动频率。我们还报告了基态到第一激发三重态跃迁能量。我们的结果与文献中可用的结果进行了分析，以说明我们所采用方法的有效性。我们还证明，通过使用适当的选择稠环间隔物来分离 TME 的烯丙基基团，可以操纵不相交的、类似 TME 的双自由基的基态的自旋特性。
