From owner-chemistry@ccl.net Wed May 31 14:58:00 2006
From: "Jozsef Csontos jozsefcsontos|a|creighton.edu" <owner-chemistry{:}server.ccl.net>
To: CCL
Subject: CCL: negative bsse content
Message-Id: <-31875-060531145149-23464-wVyHGiFQEfUrpTWJ8TpocA{:}server.ccl.net>
X-Original-From: Jozsef Csontos <jozsefcsontos-x-creighton.edu>
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Date: Wed, 31 May 2006 13:51:39 -0500
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Sent to CCL by: Jozsef Csontos [jozsefcsontos%%creighton.edu]
Hi Tanja,


> Dear Joszef,
>  
> BSSE is a negative quantity: it is calculated as the difference between 
> the sum of the monomer energies calculated in the dimer basis set and 
> the sum of the monomer energies calculated in the monomer basis set, all 
> of these at the geometries they adopt in the complex. 
> Perhaps some formulas can help
> (with latex-style sub- and superscripts):
> 
> BSSE = E_{A}^{AB}(AB) + E_{B}^{AB}(AB) - E_{A}^{A}(AB) - E_{B}^{B}(AB)

you are right, equations can help, sorry for neglecting them.
I calculated the interaction energy according to the original
Boys-Bernardi procedure:

DeltaE(CP)=E_{AB}^{AB}(AB) - E_{A}^{AB}(AB) - E_{B}^{AB}(AB)

in this case the non corrected interaction energy is 
DeltaE(noCP) = E_{AB}^{AB}(AB) - E_{A}^{A}(A) - E_{B}^{B}(B)

The difference between the two is the bsse content, which is the same as
you stated above.

Some words about the sign, I think the sign of the bsse is the matter of
definition:
(+) JCC, 25, 1771, 2004
(-) JCC, 22, 196,  2001

I used the DeltaE(CP)-DeltaE(noCP) equation which implies that the bsse
is positive. This gave me results with opposite sign comparing to yours:

> DeltaE(CP) = DeltaE(noCP) - BSSE
> 
As you might noticed, I didn't correct for deformation (fragment
relaxation), but it vanishes anyway when you subtract the interaction
energies.

So, apart from the signs, I should always get results on the same side
of zero, but I didn't.

Best wishes,

Jozsef

PS.: I tend to accept Marcin's opinion.

>I wouldn't be suprised if subtle changes in the shape of localized
>orbitals and effective partition of space between separate computations
>could actually transform some small positive net effect into small
>negative.

-- 
Jozsef Csontos, Ph.D.

Department of Biomedical Sciences
Creighton University,
Omaha, NE