A simple method of identifying π orbitals for non-planar systems and a protocol of studying π electronic structure

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The characteristic of π electrons has a crucial role in determining various properties of chemical systems, such as reactivity, aromaticity and spectroscopy. There are a large number of methods could be used for investigating π electronic structure, for example, the well-known electron localization function and multicenter bond order. For completely planar systems, the π molecular orbitals can be unambiguously identified and thus studying their π electronic structure is easy. However, for non-planar systems, identification of π orbitals and then analysis of π electrons are often not trivial. In this work, based on localized molecular orbitals (LMOs), we propose a conceptually simple and easy way to automatically identify π orbitals for any kind of systems, which makes subsequent analyses of π electrons straightforward. In addition, we show that the identified π LMOs can also be used to reliably estimate π component of molecular orbitals or other kinds of orbitals. The method proposed in this work has been implemented into our wavefunction analysis code Multiwfn as a key ingredient of standard analysis protocol for π electrons. Application examples given in this article illustrated that this protocol makes analysis of π electronic structure for a wide variety of chemical systems unprecedentedly convenient and reliable.

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Correspondence to Tian Lu.

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Lu, T., Chen, Q. A simple method of identifying π orbitals for non-planar systems and a protocol of studying π electronic structure. Theor Chem Acc 139, 25 (2020) doi:10.1007/s00214-019-2541-z

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  • Orbital localization
  • Electron structure
  • Electron localization function
  • Multiwfn
  • Localized orbital locator
  • Electron density
  • π electron
  • Bond order