Bader leapt into the fray with a polemic against Frenking’s review that even
aficionados of the wavefunction must concede is amusing and erudite. He defended
earlier work by Schr€odinger and by Slater which argued in effect that the sole use of
the wavefunction is as a mathematical device to determine the electron density
distribution [5]. He countenanced the much-criticised conclusion of the Feynman
force theorem and the virial theorem that the chemical bond is in fact simply the
result of overlap charge density, and bolstered his argument by invoking (to many
chemists no doubt recondite) work by Schwinger and Dirac, and stated clearly that
“chemistry is the interaction of the density with the nuclei; there is nothing else, at
least not in real observable space...” The statement “To ascribe an existence to a
wavefunction that controls rather than predicts the evolution of a physical system
introduces an unnecessary and unwelcome element of metaphysics.” is very reveal-
ing, emphasizing Bader’s conviction that the wavefunction is not “real”; indeed,
two sentences earlier reference is made to the abstract Hilbert space, where the
wavefunction frolics.
A long paper by Frenking et al. [6] elicited another polemic from Bader [7].
Frenking et al. presented an energy partitioning analysis of bonds in nonpolar
molecules, dividing bonding into terms represented by Pauli repulsion, electrostatic
interactions, and orbital interactions. Bader dismissed the concept of energy parti-
tioning as lying “beyond the boundaries of physics” then turned his fire on what he
considered to be errorswithinphysics engendered by that concept. He criticised a
perceived misunderstanding of the difference between electron density and the
Laplacian (r^2 ) of electron density (a Bader hallmark) which led to the assertion
by Frenking et al. that covalent bonds do not necessarily exhibit an accumulation of
electronic charge between the nuclei; Bader countered that bonded atoms experi-
ence “no Feynman force, neither attractive nor repulsive, [acting] on the nuclei
because of the balancing of the repulsive and attractive forces by theaccumulation
[emphasis in the original] of electron density in the binding region...” In a short final
(?) repartee, Frenking et al. [8] rebuke Bader for his derisive tone and defend their
understanding of electron density and its Laplacian. They argue that acknowledging
different types of bonding is fundamentally important to chemists, implying that a
rejection of the concept of energy partitioning would obviate such differentiation.
In support of this they cite Bader’s assertion that there is no difference between the
bonding in H 2 and that between theortho-hydrogens in the transition state for
biphenyl rotation, and the finding that Bader’s atoms-in-molecules (AIM) theory
gives similar bonding for He 2 and H 2. Since chemists regard bonding in H 2 as being
qualitatively different from that in the other two species, “Bader’s orthodox under-
standing of physics is unable to address fundamental questions of chemistry!” It is
contended that Bader’s reductionism does not recognize that chemistry needs its
own models, and that “Chemical research begins where the physics of Richard
Bader ends.” [emphasis in the original]. (For polemics concerned with AIM and
H–H bonding in biphenyl and related systems see [9–11]).
So where does all this leave us in trying to respond to “It is sometimes said that
electron density is physically more real than a wavefunction. Do you agree? Is
something that is more easily grasped intuitively necessarily more real?” To argue
Answers 637