Subject: DFT is over !/? (expert opinion SUMMARY)

From: Artem Masunov <[email-masked]>
Date: Tue, 27 Mar 2001 21:38:49 -0500 (EST)

Many thanks to Drs. Grimme, Rassolov and Lewars for making it clear.
Nothing is perfect, including Coulomb-hole.
 Although the difference between 3 parameters in B3LYP and 12 parameters
in Coulomb-hole approach does not seem that drastic to me..

Artem

The original question was:

>  I just became aware of the recent paper by Clementi et al. (see the
> relevant abstracts below). It seems to me that the quest for
> correlation functional is over: Clementi just did it (without any
> density, but with many empirical parameters). He...He, water trimer, and
> atomization energies to +/- 0.05 kcal/mol sound pretty convincing.

----------------------------------------
From: E. Lewars <[email-masked]>

It seems to me that if this work refers to an *empirical* functional then the
quest is not over. We want a *theoretically derived* functional with no
empirical parameters.

----------------------------------------
From: Vitaly Rassolov <[email-masked]>

I'm a bit familiar with the Clementi approach, and I don't like it
(admittedly, without knowing some of the details).  One can parametrize
almost anything.  The physics behind the parameters is pretty murky (if it
exist).  To me, scientists should simplify things, if possible.  16
parameters don't do that.  And this ridiculous accuracy of .05 kcal is a
proof that it is data fitting, not interaction description.

----------------------------------------
From: Stefan Grimme <[email-masked]>

I recently had the opportunity to talk with Clementi about his approach
and I also read a recent preprint (I think the one you mentioned). I'm not
really convinced that the Coulomb-hole approach with a lot of parameters
represents a reasonable quantum chemical approch. The main points of my
criticism are as follows:
 1. The dispersive interactions are modelled by an empirical formula which
means that the approach is not more than a combination of force field
technology and QM in that respect, i.e. its a new version of QM/MM.
 2. The Coulomb-hole (CH) improves on the HF atomization energies but does
NOT improve the relative energies which we are most interested in
(Clementi strongly emphasizes on atomisation energies but forgot to look
to the relative energies!). Simple organic reaction energies are even
WORSE with the CH-HF method compared to HF. Even the simplest DFT's
perform better in that respect.
 3. An important part of the new CH-HF formalism is based on Mulliken
charges and bond orders. We all know the problems associated with this
approach (strong basis set dependence) and I therefore expect that each
basis set would need its own parametrization (this problem has not been
discussed in the paper I know).
 4. Some time ago we tested a simpler (meaning a smaller number of
parameters) version of CH-HF for He and H-. The result was that the radial
densities were even worse than those from HF when compared with almost
exact densities.  My impression was that the basic correlation effects are
NOT included accurately, even not in a qualitative manner. Again, DFT
improves upon HF, at least qualitatively. Thus, I don't expect any
improvement for properties with the CH-HF method (I think this question is
important and Clementi has to investiagte this. We know that DFT does not
only improve energies but also properties like dipole moments etc.; the
reason is simply that the DFT densities are on the whole better than HF
densities).
 In summary I think the approach is worth while testing it but I don't
think that "the quest for correlation functional is over".

--

     __    ___________       [email-masked]; Tel 212-650-7792
    /  \  /  __   __  \     Computational Biophysical Chemistry Group
   /    \/\  \ \  \ \  \        Chemistry Dept, City College, CUNY
  /  /\  \ \  \ \  \ \  \    J-1325, Convent Ave, New York, NY 10031
 /  ____  \ \  \ \  \ \  \ -------http://www.biosys.net/artem----------
/__/\ _/\ _\ \ _\ \ _\ \ _\ FORGIVE MY NONSENSE AS I ALSO FORGIVE THOSE
\ _\/  \/__/\ __/\ __/\ __/ WHO THINK THEY TALK SENSE  --  ROBERT FROST