Chagas Julio C V, F Dos Santos Luan G, Nieman Reed, Aquino Adelia J A, do Monte Silmar A, Plasser Felix, Szalay Péter G, Lischka Hans, Machado Francisco B C
Department of Chemistry, Aeronautics Institute of Technology, São José dos Campos 12228-900, Brazil.
Advanced Scientific Computing and Modeling Laboratory, Aeronautics Institute of Technology, São José dos Campos 12228-900, Brazil.
Phys Chem Chem Phys. 2025 Apr 9;27(15):7916-7928. doi: 10.1039/d5cp00339c.
In this work, the electronic spectra of all- polyenes, from hexatriene to dodecahexaene are investigated. Special attention is given to the challenging description of the ionic 1B+u state. A comprehensive wavefunction analysis of both singlet (2A-g, 1B+u, and 2B-u) and triplet excited states (1A-g and 1B-u) is performed using a range of multireference correlated methods, including multireference configuration interaction with singles and doubles (MR-CISD) including size-extensivity Pople correction (+P), and the multireference averaged quadratic coupled-cluster (MR-AQCC) method. While covalent states are well described by multi-configurational self-consistent field (MCSCF) theory, accurately describing the ionic state requires addressing size-extensivity errors, basis set effects, and, most importantly, σ-π electron correlation. Taking these factors into account, MR-CISD+P and MR-AQCC results mutually corroborate that the ionic 1B+u state is the first vertically excited state in hexatriene and octatetraene. In decapentaene, extrapolated MR-CISD+P results indicate that the 2A-g and 1B+u states are nearly degenerate, while MR-AQCC suggests that the ionic state lies approximately 0.2 eV below the covalent state. From a wavefunction perspective, the ionic state is consistently well-represented by a single HOMO-LUMO excitation, whereas the contribution of doubly excited configurations increases with chain length for both covalent states.
在这项工作中，研究了从己三烯到十二碳六烯的全多烯的电子光谱。特别关注了离子1B+u态的具有挑战性的描述。使用一系列多参考相关方法对单重态（2A-g、1B+u和2B-u）和三重态激发态（1A-g和1B-u）进行了全面的波函数分析，包括带有单双激发的多参考组态相互作用（MR-CISD）并包含尺寸扩展性的波普尔校正（+P）以及多参考平均二次耦合簇（MR-AQCC）方法。虽然共价态可以通过多组态自洽场（MCSCF）理论得到很好的描述，但准确描述离子态需要解决尺寸扩展性误差、基组效应，最重要的是σ-π电子相关性。考虑到这些因素，MR-CISD+P和MR-AQCC的结果相互证实，离子1B+u态是己三烯和辛四烯中的第一个垂直激发态。在癸五烯中，外推的MR-CISD+P结果表明2A-g和1B+u态几乎简并，而MR-AQCC表明离子态比共价态低约0.2 eV。从波函数的角度来看，离子态始终可以由单个HOMO-LUMO激发很好地表示，而对于两个共价态，双激发组态的贡献都随着链长的增加而增加。
