An Experimentalist's Reply to “What Is an Atom in a Molecule?”

Abstract

Parr, Ayers and Nalewajski have opined in this Journal that the concept of an atom in a molecule "is an object knowable by the mind or intellect, not by the senses." This view is countered by the two hundred years of experimental chemistry underlying the realization that the properties of some total system are the sum of its atomic contributions. This paper concludes that an experimentalist has no doubt but that he or she is measuring the properties of atoms when performing an experiment.

ACKS2: Atom-condensed Kohn-Sham DFT approximated to second order

“…Split-charges are not defined as atoms-in-molecules (AIM) 72,73 quantities that can be computed directly from the electronic density or wavefunction. If such a definition would be available, one could try to approximate the DFT energy in terms of split charges and construct an EEM-like model.…”

The conformational sensitivity of iterative stockholder partitioning schemes

“…With the quantum mechanical description of the electronic many-body systen, one can model molecular properties without ever assigning electrons to certain atoms. It is even far from trivial to partition the electronic density (or wavefunction) into atomic contributions based on theoretical arguments [1,2].…”

“…This is of critical importance for the chemical interpretation of AIM properties or for the derivation of transferable force field parameters. For example, the quantum theory of atoms in molecules (QTAIM) scheme proposed by Bader [8] yields transferable AIM properties [2,9]. On the other hand, charges fitted to reproduce the molecular ESP are traditionally not robust.…”

QTAIM and NBO Analysis of a New Oxidative Salt of 1,1/-(Ethane-1, 2-diyl) Dipyridinium bisiodate

“…QTAIM-based analysis of electron density at different characteristic points, particularly at the bond critical points(BCP), is a powerful tool for investigation of different Chemical or physical phenomena [17][18][19][20][21][22] . It is well proved that the magnitude of the electron density function estimated at the BCP can reflect the strength of a given bond.The results of the topological analysis ( Figure 5) for the In the theoretical charge density studies we have calculated the local potential energy density U(r BCP ) and kinetic energy density G(r BCP ) at BCPs essentially to represent a quantity proportional to the non-covalence bond energy.…”