Subject: Re: CCL:Why aren't DFT methods suitable for long distance interactions?

From: csonka <[email-masked]>
Date: Fri, 15 Oct 1999 09:34:12 +0200

Dear Yubo Fan and CCL readers,

I agree with the opinion of  Lou Noodleman. DFT in the form of gradient
corrected potentials (GGA) has
proved suitable for many applications involving H-bonds. (LSDA is not
suitable).
I would like to add one probably important success of GGA-ACM-DFT: the
description of OH...O interactions in sugar molecules.
The following paper discusses some details:
G.I. Csonka et al: Chem. Phys. Lett. 257 (1996) 49-60.

futher references can be found on my home page.

It is also true that that quite weak H-bonds are difficult for DFT. Weak
long range Van der Waals interactions
(dispersion energies) are missing from DFT.

Walter Kohn was working on dispersion energies within DFT framework
(DFT97, Wienna). Also John Perdew had some interesting papers about the
long range interactions.

Gabor I. Csonka              Budapest University of Technology
FAX: (361) 463.36.42         Inorganic Chemistry Dept. Ch. Bldg
[email-masked]        H-1111, Bp. Szent Gellert ter 4
http://web.inc.bme.hu/~csonka/csg.html
http://www.ch.bme.hu/inc/csg.html

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From: "Dr. Martin Schuetz" <[email-masked]>
Date: Fri, 15 Oct 1999 11:13:56 +0200 (MDT)

One should be aware, that the dispersive contribution to a hydrogen bond
of the type H2O-H2O is about 20 %, hence far from negligible. (this can
e.g. be seen in SAPT or local correlation calculations). Therefore, one
should be aware, that the relatively good agreement between GGA DFT
methods and MP2 is fortuitious, i.e. a result of error cancellation.
A good choice and reliable method for describing hydrogen bonded systems
is MP2.

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From: WeiQuan Tian <[email-masked]>
Date: Fri, 15 Oct 1999 09:38:15 -0400 (EDT)

There is a paper of Dr. Weitao Yang : J. Chem. Phys. 107(19), 7921-7925,
1997 for the analysis of GGA on van der Waals interaction. Actually in the
normal case ( except the pure disperion interaction), there are charge
transfer, static electric interaction and so on. Also, the performance of
GGA on such interaction is individual. 

 Wei Quan Tian

On Fri, 15 Oct 1999, Dr. Martin Schuetz wrote:

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From: [email-masked]
Date: Fri, 15 Oct 1999 15:16:18 -0400 (EDT)

Dear CCLers
        To add to the conversation about DFT and long distant interaction
I thought I may give and example.
        Recently, we did calculations on metal-rare gas dimers using HF,
B3LYP, and MP2 thoeries implementing a large basis set.  On the
neutral dimers, which are bound by dispersion forces, HF and B3LYP did
not locate bound states as where the MP2 calculations were able to do
so.  As the electrostatic contribution to the dimerization
energy increased, by removing the metal's valence electrons, HF theory was
able to locate bound states.  B3LYP also located bound states but only
after the electrostatic contibution became relatively larger.  HF theory
underestimated the binding of the charged dimers, as
expected since HF theory does not include dispersion forces.  B3LYP, which
should follow a similar trend as HF, actually overestimated the binding
energy relative to the MP2 values.  The result of these calculation are
presented in a paper which is about to be sent out for peer review in J.
Chem. Phys..
	For calculations, getting the right answer for the right reason is
difficult to do.  As pointed out earlier, often the good agreement with
experiments are done due to fortuitous cancellations of error.  The right
reasons include convergence of all component to the dimerization energy
(ie. dispersion, electrostatic, etc.) basis set convergence, valence
versus valence plus core electron correlation, and BSSE (to correct for or
not to correct for...) to name a few.  To understand the approximations in
the method is to understand the validity of the results.

An excellent book on Hydrogen bonding that disscusses much of these
issues:
1) S. Scheiner, Hydrogen Bonding, A Theoretical Perspective, Oxford
University Press, 1997.

Some papers relevant to DFT calculations of dispersion forces:
1) S. Kristyn and P. Pulay, Chem. Phys. Lett. 229, 175 (1994).
2) J. M. Perez-Jorda and A. D. Becke, Chem. Phys. Lett. 233, 134 (1995).
3) P. Hobza, J. Sponer and T. Reschel, J. Comput. Chem. 16, 1315 (1995).
4) D. C. Patton and M. R. Pederson, Int. J. Quantum Chem. 69, 619 (1998).
5) J. M. Prez-Jord, E. San-Fabin and A. J. Prez-Jimnez, J. Chem. Phys.
110, 1916 (1999).

A paper for MP2 and dispersion (Ar2 dimer):
1) D. E. Woon, Chem. Phys. Lett 204, 29 (1993).

Hope this adds constructively to the conversation.
Sincerely,
Karl

_______________________________________________________________________________
				   |
Karl Nicholas Kirschner            |e-mail: [email-masked]
Computational Center for           |web: http://charon.chem.uga.edu/~karl
   Molecular Structure and Design  |"...Experience is not what happens to a
University of Georgia - Athens     |man.  Experience is what a man does with
				   |what happens to him." Knox
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