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Welcome to the second edition of the Unusual ChemBond Challenge @[edit]

The literature is full of controversial molecules, which present unusual bonding situations that often are interpreted in a completely different way depending on the tools used for the analysis. In 2017, we asked for your help to review some interesting cases in the first edition of the Unusual Bonding Slam that we organized as part of the Chemical Bonds at the 21st Century conference held in Aachen, a satellite meeting to the WATOC 2017 conference.

This year we are organizing the second edition as part of the ESCB2 conference held in Oviedo. There are many chemical bonding tools that help to get an insight of the electronic structure of molecules but, in certain situations, some of them offer conflicting views or are pushed beyond its own limitations. One of the most useful and controversial types of techniques is the energy partition. There are many schemes of energy decomposition: from real space decomposition such as the interacting quantum atoms (IQA) and similar approaches,[1][2][3][4][5][6], variational methods such as the energy decomposition analysis (EDA)[7][8][9][10] and ALMO EDA,[11] pertubation-theory based including the symmetry-adapted perturbation theory (SAPT),[12] and methods based on localized orbitals such as the natural bond orbitals (NBO),[13] and natural orbital for chemical valence (NOCV).[14][15]

The total energy of a quantum system is expressed as the sum of kinetic and potential energy terms which satisfy or not the virial theorem in actual calculations according to the method used for the calculation (to my knowledge the virial theorem has only been established in the literature for exact and Hartree-Fock wave functions, other functions require a scaling). The kinetic and potential energy terms are both physically unambiguously defined and therefore physically consistent. The contributions to the potential energy (Coulombic (HF, post HF, DTF), exchange (HF), correlation (post HF), exchange-correlation (DTF), electrostatic, induction, dispersion (perturbation theory of intermolecular interactions), ionic, covalent, resonance, charge-shift (VB)) are all determined by the calculation scheme or/and by an underlying representation. There is no equivalent of the virial theorem providing relationships between these terms. However, their actual values are often considered in the discussion of the bonding in a given system. Beyond this, quantum chemists often express each energy component in terms of orbital or atomic contributions.[8][16][10][17][18][3][2]

Energy decomposition techniques are often used to characterize and discuss the bonding. As there is not a unique method, each decomposition scheme has its own strengths and its own weaknesses. Energy decomposition belongs to a reductionist rather than holistic strategy. What is the epistemological status of these approaches, particularly with respect to demarcation criteria (Popper, Lakatos,..)?

We expect your feedback! Join the discussion!


In creating your user account for this Wiki using this link please also populate e.g. with some information about yourself (such as e.g. your ORCID registered at Anonymous contributors will not be selected for the bond slam.

When making a contribution to a page, please use the Button sig.png icon from the editor bar to insert your identification and to reveal the date of your edit.

Useful simple hints for enhancing the Wiki pages[edit]

  • Use e.g. <ref>M. Malischewski, and K. Seppelt, ''Angewandte Chemie International Edition'', '''2016''', ''56'', 368-370. {{DOI|10.1002/anie.201608795}}</ref> when editing/contributing in order to cite references and have them auto-renumber.[19].
    • The template {{DOI|10.1002/anie.201608795}} can be used to insert a DOI in the manner shown.
  • A PDF file can be first uploaded and then inserted using e.g. [[file:name-of-file.pdf|200px]]
  • Use e.g. <jmolFile text="Click to view 3D molecular model">TOQKIT.mol</jmolFile> to create a link to view a previously uploaded molecular coordinate file.
    • A more elaborate invocation is shown here, allowing a script to control the appearance of the 3D molecule display: <jmol><jmolApplet><title>CH3F(2-)</title><color>white</color> <size>200</size><script>frame 9;vectors 4;vectors scale 2.0;color vectors red;vibration 10;</script> <uploadedFileContents>CH3F.log</uploadedFileContents> </jmolApplet></jmol>
  • If you have a quantum calculation that you wish to offer in evidence of any discussion, consider depositing it into a data repository and quoting the assigned DOI here so that we can all have access to the details of the calculation. Suitable repositories might be Figshare, Zenodo or institutional repositories that assign DOIs.
  • If you wish to change your password or other preference, login in using your existing password and then click on Preferences to make your changes.
  • Hint: if you are editing the source of any page with your own (and others) contributions, you might want to copy/paste the source into a local text file as your backup as a precaution.


  1. To get a snapshot of how much editing activity is associated with any challenge, visit Conference activity via page revisions.
  2. For statistics, visit here
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  1. A. Martín Pendás, M. A. Blanco, E. Francisco, J. Chem. Phys. 2004, 120, 4581. DOI:10.1063/1.1645788
  2. 2.0 2.1 M. A. Blanco, A. Martín Pendás, E. Francisco, J. Chem. Theory Comput. 2005, 6, 1096. DOI:10.1021/ct0501093
  3. 3.0 3.1 E. Francisco, A. Martín Pendás, M. A. Blanco, J. Chem. Theory Comput. 2006, 2, 90. DOI:10.1021/ct0502209
  4. P. Salvador, M. Duran, I. Mayer, J. Chem. Phys. 2001, 153, 1153. DOI:10.1063/1.1381407
  5. P. Salvador, I. Mayer, J. Chem. Phys. 2004, 120, 5046. DOI:10.1063/1.1646354
  6. P. Salvador, I. Mayer, J. Chem. Phys. 2007, 126, 234113. DOI:10.1063/1.2741258
  7. F.M. Bickelhaupt, E. J. Baerends, Rev. Comput. Chem. 2000, 15, 1. DOI:10.1002/9780470125922.ch1
  8. 8.0 8.1 K. Morokuma and K. Kitaura, Molecular Interactions, Wiley and sons, Chichester, 1980, vol. I, 21–66
  9. K. Morokuma, J. Chem. Phys. 1971, 55, 1236. DOI:10.1063/1.1676210
  10. 10.0 10.1 S. Dapprich, G. Frenking, J. Phys. Chem., 1995, 99, 9352
  11. Y. Mao, P.R. Horn, M. Head-Gordon, Phys. Chem. Chem. Phys. 2017, 22, 5944. DOI:10.1039/c6cp08039a
  12. K. Szalewicz WIREs Comput Mol Sci. 2012, 2, 254. DOI:10.1002/wcms.86
  13. A. E. Reed, L. A. Curtiss, F. Weinhold, Chem. Rev. 1988, 88, 899. DOI:10.1021/cr00088a005
  14. A. Michalak, M. P. Mitoraj, T. Ziegler, J. Phys. Chem. A 2008, 112, 1933. DOI:10.1021/jp075460u
  15. M. P. Mitoraj, A. Michalak, T. Ziegler, J. Chem. Theory Comput. 2009, 5, 962. DOI:10.1021/ct800503d
  16. I. Mayer, Int. J. Quantum Chem. 1983, 23, 341.
  17. A. W. Ehler, G. Frenking, J. Am. Chem. Soc., 1994, 116, 1514.
  18. M. P. Mitoraj, A. Michalak, T. Ziegler, J. Chem. Theory Comput. 2009, 5, 962. DOI:10.1021/ct800503d
  19. M. Malischewski, and K. Seppelt, Angewandte Chemie International Edition, 2016, 56, 368-370. DOI:10.1002/anie.201608795