Subject: BSSE sign summary response

From: Tankiso Tshehla - PG <[email-masked]>
Date: Wed, 5 Jul 1995 16:28:42 +0200 (SAST)

To all the netters;

While I will be summarising the responses, I would like to thank all 
who responded. The general view  is that this should not have 
happened, if it did may something was not correct in the beginning. 
Or perhaps the basis set in incomplete.

The reason I posted the meassage was simply because I did not believe 
the results I was getting. I am glad that through the different views 
>from CCL I finally got the solution.
I ran the massage job once more with completely new input and it 
worked. I suspect that one of the parameters might have been wrong. 
        Thanks to all
          T M Tshehla

Summary

charles W Ulmer, II Ph. D.
wrote:
I wouldn't want to begin to answer your question without knowing more 
about the way in which you calculated the BSSE. ref to

Nagy, P. I. C. W. II; Smith, D.A J. Chem. Phy. 1995, 102, 6812.

David E. Woon wrote:
You shouldn't be able to get negative BSSE from the counterpoise 
correction (assuming you are using full CP correction). The monomers 
in the dimers basis set must have lower energies than their 
respective monomer sets. Since it sounds like you're optimising the 
monomer geometries in the dimer basis, you also add a correction for 
that, even if the change is small.

R. G. A. Bone Ph D. wrote:

The only thing you can really do is to increase the size of the basis 
set--- substantially for a correlated level calculation.

There may be other ways of compensating for BSSE at the MP2 level, 
other than using the CP correction; this is still an open issue.

M A Zottola wrote:

are you sure that:
1) The Z-matrix describing your system is correct-

2) you subtracted the sum of the counterpoise-calculated monomer 
energies from the the energy of the complex-

3) You are using the Mp2 energies not the HF energies for the calc. 
of dE

I have never seen a negative correction from BSSE - indeed that 
observation contradicts the concept of superposition error. good luck 
in ferreting out an answer!

      all   all      all     all