Subject: BSSE and semi-empirical methods

From: "Schiffer, Heinz, Dr., WIA / SC" <[email-masked]>
Date: Fri, 18 Oct 1996 17:12:47 +0200

Some time ago, I posted the following question to the list :

>Dear netters,
>I am thinking about the calculation of the BSSE with semi-empirical 
methods.
> As far as I understand the whole thing, the BSSE is largest with minimal 
basis sets.
>Therefore I expect large BSSEs with semi-empirical methods. It would be 
very nice
>to hear your opinion on that. On the other hand : Does it make sense at all 
to compute
> weak interactions with semi-empirical methods ?
>Ciao,
>Heinz

I want to thank everyone who responded. Besides the contribution of Dr. Shah 
Nilar
>from the University of Alberta ( Canada ), which was already on the list (
24.9.96 ),
and with whom I agree completely, I got the following answers :

=======================================================================

>From :

Francois HUTSCHKA
Ph.D. Student in QuantumChemistry 

Laboratoire de Chimie Quantique
UPR 139 du CNRS
4, rue Blaise Pascal                       Phone:  (33).88.41.60.32
67000 STRASBOURG                  Fax:    (33).88.61.20.85
FRANCE                                            E-Mail: 
[email-masked]

Heinz,
Regarding to your question about the BSSE, you should take a look at the
following paper:
B. Kallies, R. Mitzner, J. Mol. Model. 1995, 1, 68-78
you can download the paper in .pdf format through:
http://derioc1.organik.uni-erlangen.de/info/JMOLMOD/papers/papers.html
You can also look at :
V. Parasuk, J. Almlof, B. Deleeuw, Chem. Phys. Lett. 1991, 176, 1-6
I hope this will help you
Best regards
Francois.

=======================================================================

From:

Guillermo A. Morales, Ph.D.
The DuPont-Merck Pharmaceutical Company
TEL: 695-1053                  <MORALEGA@A1@LLDMPC>

Dear Heinz,
Interesting questions. Could you please send me a summary of all the answers 
you
get? I'll appreaciate that a lot.
Guillermo.

=======================================================================

>From :

John Gunn ([email-masked])
Departement de Chimie / CERCA
Universite de Montreal

Hi,
This is not a response, but I would be interested in seeing a summary
of the replies you receive.  I have in fact been working on a correlated
semi-empirical method for weak interactions which doesn't use a basis
set at all.  I don't have much experience though with BSSE for traditional
HF-SCF-LCAO type methods.
 -John.

=======================================================================

>From :

Tim Clark

   . actually, there is essentially no BSSE in semiempirical methods
     because (a) the two-electron integrals are scaled down to take dynamic
     correlation into account and (b) the minimal basis set uses Slater
     orbitals, which have far better "tails" than Gaussians. These two 
factors
     mean that the e-:e- repulsion is not overestimated as it is in
     conventional Hartree-Fock theory and that the diffuse areas of the
     space around the atoms are treated better by the basis functions.
     BSSE is an artefact of the finite basis set and the mean field
     approximation.

=======================================================================

>From :

Knut Krause
Institut fuer Physikalische Chemie
Bundesstrasse 45
20146 Hamburg
Germany
Tel: # 040/4123-3428
Fax: # 040/4123-3452
E-mail: [email-masked]

Dear Heinz,
I haven't heard about calculating the BSSE with semiempirical methods yet
and I guess there are two reasons why:
1. The basis set used in semiempirical methods is not as bad as you suppose, 

because normally slater functions are used with semiemp. calculations in
contrast to the use of gaussian functions in ab initio calculations.
The only advantage of the gaussians is the easy calculatins of orbital
overlap integrals.
2. Since the calculation of the orbital overlap is simplyfied or neclected
in semiempirical methods, the calculation of the weak interaction between
molecules is not very accurate, I suppose.
I hope this helps and I am looking forward to a further discussion.
Knut

=======================================================================

>From :

Robert J. Gdanitz                                               email: 
[email-masked]
GhK |  Gesamthochschule Kassel                Tel.: +(49) 561-804-4556
Fachbereich 18 (Physik)                                  Fax:  +(49) 
561-804-4006
D-34109 Kassel, Germany

Lieber Heinz,
ich betrachte mich nicht gerade als Experten zur Beantwortung Deiner Frage,
aber nach meinem derzeitigen Kenntnisstand wuerde ich folgendes dazu sagen:
Semiempirische Methoden benutzen meist Minimalbasen, was zur Folge hat, dass
eigentlich nur der statische Beitrag der Elektronenkorrelation erfasst wird.
Da die Dispersions-WW nur durch den dynamischen Anteil der Korrelation 
zustande-
kommt, wuerde ich hier kein sinnvolles Ergebnis erwarten. Weiters sollte der
BSSE sehr klein sein, denn es gibt keine Funktionen, die am anderen Zentrum
gute Korrelationsorbitale darstellen.
Andererseits ist in der Semiempirik dynamische Korrelation 
mitparametrisiert.
So gesehen koennte es unter gewissen Umstaenden moeglich sein, brauchbare
Ergebnisse zu bekommen. Also, es hilft nur eins: Ausprobieren!
Beste Gruesse,
Robert

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Dr. Heinz Schiffer                          65926 Frankfurt am Main
Hoechst AG               Phone ++49-69-305-2330
Scientific Computing          Fax       ++49-69-305-81162

Email :   [email-masked]
     [email-masked]
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