Subject: CBS AND G2 FAILURE-SUMMARY; THANKS

From: "E. Lewars" <[email-masked]>
Date: Mon, 22 Mar 1999 13:42:41 -0500 (EST)

1999 March 22     CBS and G@ METHODS FAILING

Thankd to all who replied to my question (below) about problems with CBS and
G2 methods. I give a summary of the answers
   Again, thank you all.

       E Lewars
==================
THE QUESTION:

1999 March 14

Hello,

I find that the high-accuracy G2-type (G2, G2MP2 etc) and CBS (CBS-4,
CBS-Q) methods, as implemented in Gaussian 94 and Gaussian 98, useful as they
are, fairly frequently fail because of convergence problems. G92MP2 fails in
step 5, and CBS-Q and CBS-4 in step 4, that is, after wasting hours on several
previous steps.

If others have had this problem with G2 and CBS methods and found a solution,
I would very much appreciate hearing what it is.

  Thank you.
    E. Lewars
==========================
THE ANSWERS

#1

          Mar 14 Giovanni Scalmani  (52)   Re: CCL:G:G2 AND CBS METHODS: CONVECommand: Read MessageMessage 3/10 from Giovanni Scalmani                      Mar 14 '99 at 6:28 pm

X-Sender: [email-masked]
Subject: Re: CCL:G:G2 AND CBS METHODS: CONVERGENCE FAILURES

On Sun, 14 Mar 1999, E. Lewars wrote:

> I find that the high-accuracy G2-type (G2, G2MP2 etc) and CBS (CBS-4,
> CBS-Q) methods, as implemented in Gaussian 94 and Gaussian 98, useful as they
> are, fairly frequently fail because of convergence problems. G92MP2 fails in
> step 5, and CBS-Q and CBS-4 in step 4, that is, after wasting hours on several
> previous steps.

Hi!

  You are not talking about the SVD (singular value decomposition) 
in link 803, aren't you? (I don't remenber the exact sequence of steps).

 Anyway, once I had problems with CBS-Q and - even worse - with
CBS-APNO. They failed "after wasting hours" during SVD. So I modified
the code to use the LAPACK SVD routine (DGESVD) instead of the 
original one and since then I never had a new failure (at least in
l803.exe).

Hope this help.

Giovanni 

PS: Let me know if this is your case. I may provide you the modification
    to l803.F

----------------------------------------------------------------------
Scalmani Giovanni                           [email-masked]
Service de Chimie des Materiaux Nouveaux
Centre de Recherche en Electronique et Photonique Moleculaires
Universite' de Mons-Hainaut
Place du Parc, 20                             Phone: ++32-(0)65-373361
B-7000 Mons (Belgium)                           Fax: ++32-(0)65-373367
----------------------------------------------------------------------
==============

#2

Subject: RE: G:G2 AND CBS METHODS: CONVERGENCE FAILURES
Date: Mon, 15 Mar 1999 08:38:44 +1000

Greetings,...

>I find that the high-accuracy G2-type (G2, G2MP2 etc) and CBS (CBS-4,
>CBS-Q) methods, as implemented in Gaussian 94 and Gaussian 98, useful as
they
>are, fairly frequently fail because of convergence problems. G92MP2 fails
in
>step 5, and CBS-Q and CBS-4 in step 4, that is, after wasting hours on
several
>previous steps.

I'm not sure what 'Step 5' is in a 'G2' calculation as implemented in G94,
however, I suspect it is the QCISD calculation, something I have much
experience with (convergence problems that is).  The best alternative is to
replace the QCISD(T) with CCSD(T).

Regards,...

Brian.

 ________________________________________________________________
| Dr Brian J. Smith                                              |
| Research Scientist                                             |
| Biomolecular Research Institute                                |
| 343 Royal Parade                          Ph:  +61-3-9662-7289 |
| Parkville, VIC 3052,                      Fax: +61-3-9662-7347 |
| Australia              WWW http://www.bioresi.com.au/index.htm |
|________________________________________________________________|

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

#3

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Date: Mon, 15 Mar 1999 09:44:48 +0100
To: [email-masked]
Subject: CBS and G2

Dear Prof. Lewars,

In problem cases I usually run the jobs separately. For G2(MP2) method this
gives me the possibility of converging the SCF (using SCF=qc) in the
MP2/6-311+(3df,2p) calculation. On the other hand, the CBS extrapolation
convergence problems appear to be hard ware dependent, switching to
different hard ware brand have helped in all my problem cases.

In the end I collect the results in a spread sheet. When the implemented
method crashes in the final step, the results from the earlier steps can
also be extracted in this manner. Thus, re-running the job can be avoided.

Cheers,

                      Theis

**  **  **      **  Mr. Theis Ivan Solling
**  **   ** ** **       Department of Chemistry
******    ******        University of Copenhagen
**  **      **          DK-2100 Copenhagen
**  **      **          Ph. 45-3532-0187/Fax. 45-3532-0212 
===========