SCI: a robust and reliable density-based descriptor to determine multiple covalent bond orders

  • Ying Huang
  • Lianghong Liu
  • Chunying Rong
  • Tian Lu
  • Paul W. Ayers
  • Shubin Liu
Original Paper
Part of the following topical collections:
  1. International Conference on Systems and Processes in Physics, Chemistry and Biology (ICSPPCB-2018) in honor of Professor Pratim K. Chattaraj on his sixtieth birthday


Very recently [J. Phys. Chem. A 2018, 122 (11), 3087–3095], we proposed to employ the Pauli energy to identify and determine strong covalent interactions (SCI), whose bond order are equal to or larger than two. This is done through the signature isosurface shape between the two bonding atoms. We discovered that the signature shape for a double, triple, and quadruple covalent bond is like a dumbbell, donut (torus), and four-beats, respectively. Systems with even higher bond orders were examined and confirmed. This work is a follow-up study of our previous work. The dependence of the signature isosurface shape on the choice of methodologies and basis sets is systematically investigated. Its effectiveness and robustness in determining bond orders are highlighted again with more examples. In addition, using the molybdenum dimer in different environments, e.g., in vacuum, sandwiched between molecules, and encapsulated in the C80 cage, as illustrative examples, we show that, generally speaking, bond strength and bond order are two different chemical concepts. For systems containing transition metals, it is not always true that a short metal-metal bond length corresponds to a larger bond order. Put together, these results should provide additional pieces of convincing evidence showing that the SCI index is a robust and reliable density-based descriptor to accurately determine multiple covalent bond orders.


Strong covalent interaction Pauli energy Multiple covalent bond Density-based descriptor Quintuple bond 



SBL and CYR acknowledge support from the National Natural Science Foundation of China (No. 21503076) and Hunan Provincial Natural Science Foundation of China (Grant No. 2017JJ3201). This work is dedicated to our longtime friend, Professor Pratim K. Chattaraj of the Indian Institute of Technology Kharagpur, India, for his 60th birthday. Happy Birthday, Pratimda!


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.School of PharmacyHunan University of Chinese MedicineChangshaChina
  2. 2.Department of PharmacyHunan University of MedicineHuaihuaChina
  3. 3.Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China), College of Chemistry and Chemical EngineeringHunan Normal UniversityChangshaChina
  4. 4.Beijing Kein Research Center for Natural SciencesBeijingChina
  5. 5.Department of ChemistryMcMaster UniversityHamiltonCanada
  6. 6.Research Computing CenterUniversity of North CarolinaChapel HillUSA

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