Subject: Re: DFT METHODS, COMPARISON

From: [email-masked] (John Lohrenz)
Date: Fri, 25 Aug 1995 12:21:50 -0600 (MDT)

BLYP, B3LYP, Becke3LYP, LYP, .... 

 Thorsten Koch wrote:
>  does anyone have any references about the performance and quality of the
>diverse DFT-methods like LDSA, Becke, Becke3 ... ?
>Up to now, this are only names to me and I'd like to know which method
>should be preferred for certain purposes.

we had this discussion before (see my summary earlier this year)... 
But what did we learn from it? 
Just a few comments:

We should first of all not just refer to what is stated in the Gaussian
manual. DFT was invented much earlier and there are many other programs
(DMON, DeMOL, ADF, DeFT,... you name it) which have been applied for much longer
time than GAUSSIAN/DFT. Unfortunately the latter somewhere stated that
the Lee-Yang-Parr correction is the most reliable and since then almost
everybody is using this as kind of a benchmark. There are other and to 
my knowledge sometimes (I explicitly say sometimes) more reliable functionals.

Errol Lewars wrote:
>There was a recent question about which DFT method is best.  A quite extensive
>compilation of geometries and relative energies from four methods (SVWN/6-31G,
>SVWN/6-31G*, B3LYP/6-31G, and B3LYP/6-31G*) indicates the best of these is
>B3LYP/6-31G*: *Practical Strategies for Electronic Structure Calculations*,
>Warren J. Hehre, Wavefunction Inc., 1995 [[email-masked]].  See also
>J. E. Del Bene, W. B. Person and K. Szczepaniak, J. Phys. Chem., 99, 10705-
>10707 (1995), especially refs 1f-h.  This paper says that B3LYP fails for 
>H-bonded complexes with the 6-31G* basis.

Second, if we really want to compare the quality of the functionals we
should not mix the results of Local-Density Calculations (LDA) with
Non-Local calculations (NL). Everybody should know that LDA has certain
short-comings and compares to NL may like HF to MPx (no flames please).
Thus the better performance of B3LYP with respect to SVWN doesn't say
anything about the quality of B3LYP. Compare with Becke-Perdew, or the
hybrid-methods and so on, and we will really learn something.

 Seiji Mori wrote:

> Utility of DFT is fastly increasing in the application of DFT method .
> Now Becke3LYP is known as the best method of DFT, but I think that the 
                                ^ok, who said that?

Finally I'd like to state that one should always mention what kind of 
systems he is refering to. It is for example known, that the hybride-
methods give excellent results for main-group (mainly C,H,O,N) molecules,
but might as well fail for transtion metals.

Cheers, John

-- 
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Dr. John Lohrenz
Dept. of Chemistry                         Phone: (403) 220 3232
University of Calgary                      FAX:   (403) 289 9488
2500 University Drive, N.W.
Calgary, Alberta, T2N 1N4            email: [email-masked]
Canada
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