Subject: Are methods based on DFT ab initio? (More information)

From: "gregor t. overney" <[email-masked]>
Date: Mon, 15 May 1995 19:07:49 -0600 (MDT)

Are methods based on density functional theory (DFT) ab initio? A quick
summary
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   I am very grateful for the feedback I am currently receiving on this
issue. So far, I can subdivide the different opinions into three groups
(one more than I thought). The first one wants to have DFT-based methods
to be considered as ab initio (which is my personal opinion). The second
one likes to put it into a category placed between semiempirical and ab
initio, where some researchers still like to use the expression "from
first principles" but not "ab initio". (And I always thought that ab
initio means nothing more than from first principles). Last but not least,
the third group sees DFT-based methods to be more of a semiempirical
rather than an ab initio nature. 

   Since quite a few readers asked me to be more specific with my
statement regarding Dr. Jerzy Cioslowski's point of view, I cite from the
conclusions of a book contribution written by Dr. Jerzy Cioslowski
("Reviews In Computational Chemistry", edited by K.B. Lipkowitz and D.B.
Boyd, VCH Publishers, Inc. 1993, Volume 4, Chapter 1, "Ab Initio
Calculations on Large Molecules: Methodology and Applications"): 

   "A subject that has not been covered here is that of the methods based
on density functional theory (DFT). It is the author's view that these
methods, although without doubt having a legitimate place in quantum
chemistry, are more of a semiempirical rather than an ab initio (as often
claimed) nature. The functionals used in the DFT programs (such as DMOL
[1]) are quite simple, and it is not currently known how they can be
methodically improved. This is in contrast to the molecular orbital
methods, in which the accuracy is limited only by the available computer
resources." 

[1] B. Delley, J. Chem. Phys., 92, 508 (1990). 

   Some people have pointed out that it is not so important how we are
going to classify DFT-based methods. But I think that expressions in
quantum theory shall be exactly defined to make sure that the risk of mis-
communication is strongly reduced. 

Gregor Overney

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Gregor T. Overney, Ph.D.                           Department of Chemistry
Senior Research Associate                     The University of New Mexico
                                                Albuquerque, NM 87131-1096

Voice: (505) 277-1665                                  FAX: (505) 277-2609
                               WWW:  http://enke.unm.edu/gregor/gregor.htm
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