CCL: QTAIM or else

 Sent to CCL by: "Paul  Popelier" [pla]^[manchester.ac.uk]
 Dear Lukman:
 I do not at all agree with the statement of Prof Grimme saying that
 "I don't think that QTAIM can give you a reasonable answer because its
 predictions are in serious disagreement with experimental data for a related
 case,"
 This paper has been rebutted by Bader and also by myself in
 The QTAIM Perspective of Chemical Bonding , P.L.A. Popelier in
 The Nature of the Chemical Bond Revisited, Chapter 8, pp 271-308 (pp 1-38), Eds.
 G. Frenking and S. Shaik, Wiley-VCH, 2014.
 For your convenience let me quote a relevant passage from this Chapter:
 "Moreover, it should be emphasized that the German authors invoked the
 architecture of the MM3 force field in order to separate molecular potential
 energy into chemically meaningful parts. Of course, this is the wrong way
 around. Indeed, popular force fields such as AMBER (or MM3 for that matter) have
 little authority, if any, when it comes to partitioning energy in a physically
 rigorous manner [63, 64]. The right way around is to construct a rigorous force
 field from an actual quantum mechanical energy partitioning scheme. Pivotally,
 however, the German authors used the arbitrary energy partitioning that
 underpins MM3 to support their main argument of the repulsive nature of H...H
 interactions. There is another and, quite frankly, better route however. If one
 is happy with the main
 idea of topological partitioning, which is that of Quantum Chemical Topology
 (QCT), then one can trust IQA and proceed with it. The minimal quantity VAB xc
 that IQA offers provides a route to cut the vicious circle of interpreting
 bonding with schemes that impose bonding. Is it not safer to calculate a minimal
 and physically well-defined quantity and observe the bonding pattern it reveals
 rather than perpetuate primitive chemical intuition, by deciding a priori which
 interactions are bonds and which are not?"
 Finally, you may be interested in the very recent work of a fellow South-African
 Professor called Jan Dillen, who published a very interesting and, in my opnion,
 correct paper on the meaning of H...H BCPs.
 "Congested Molecules. Where is the Steric Repulsion? An
 Analysis of the Electron Density by the Method of
 Interacting Quantum Atoms"
 International Journal of Quantum Chemistry 2013, 113, 21432153
 Again, this work disagrees with Grimme's view.
 Good luck with your research,
 Paul
 pla+*+manchester.ac.uk