Kumar Manish, Soler-Polo Diego, Lozano Marco, Monino Enzo, Veis Libor, Jelinek Pavel
Institute of Physics, Czech Academy of Sciences, Prague 16200, Czech Republic.
Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague 2 CZ12116, Czech Republic.
J Am Chem Soc. 2025 Jul 16;147(28):24993-25003. doi: 10.1021/jacs.5c08166. Epub 2025 Jul 2.
Recent progress in on-surface chemistry has enabled the synthesis of novel polyradical molecules with interesting electronic structure, which are hardly available in solution chemistry. Moreover, the possibility to characterize their electronic structure with scanning tunneling spectroscopy (STS) with the unprecedented spatial resolution opens new possibilities to understand their nontrivial electronic structure. However, experimental STS maps of molecules on surfaces are interpreted using one-electron STM theory within the framework of one-electron molecular orbitals nowadays. Although this standard practice often gives relatively good agreement with experimental data for closed-shell molecules, it fails to address multireference polyradical molecules. In this manuscript, we provide multireference STM theory including out-of-equilibrium processes of removing/adding an electron within the formalism of many-electron wave functions for the neutral and charged states. This can be accomplished by the concept of so-called Dyson orbitals. We will discuss the examples where the concept of Dyson orbitals is mandatory to reproduce experimental STS maps of polyradical molecules. Finally, we critically review the possibility of the experimental verification of the so-called SOMO/HOMO inversion effect using STS maps in polyradical molecules. Namely, we will demonstrate that experimental STS measurements cannot provide any information in case of strongly correlated molecules about the ordering of one-electron molecular orbitals and, therefore neither about the SOMO/HOMO inversion effect.
表面化学领域的最新进展使得合成具有有趣电子结构的新型多自由基分子成为可能，而这些分子在溶液化学中很难获得。此外，利用扫描隧道光谱（STS）以前所未有的空间分辨率表征其电子结构的可能性，为理解其复杂的电子结构开辟了新的途径。然而，目前在单电子分子轨道框架内，表面分子的实验STS图谱是使用单电子STM理论来解释的。尽管这种标准做法通常能与闭壳层分子的实验数据取得较好的一致性，但它无法处理多参考多自由基分子。在本论文中，我们提供了多参考STM理论，包括在多电子波函数形式下，针对中性和带电状态移除/添加一个电子的非平衡过程。这可以通过所谓的戴森轨道概念来实现。我们将讨论一些例子，其中戴森轨道概念对于重现多自由基分子的实验STS图谱是必不可少的。最后，我们批判性地审视了利用多自由基分子的STS图谱对所谓的单占据分子轨道/最高占据分子轨道（SOMO/HOMO）反转效应进行实验验证的可能性。也就是说，我们将证明，对于强关联分子，实验STS测量无法提供关于单电子分子轨道排序的任何信息，因此也无法提供关于SOMO/HOMO反转效应的任何信息。
