From owner-chemistry@ccl.net Tue May 30 17:51:00 2006
From: "Jozsef Csontos jozsefcsontos**creighton.edu" <owner-chemistry(~)server.ccl.net>
To: CCL
Subject: CCL: negative bsse content
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X-Original-From: Jozsef Csontos <jozsefcsontos,,creighton.edu>
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Date: Tue, 30 May 2006 16:47:29 -0500
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Sent to CCL by: Jozsef Csontos [jozsefcsontos[a]creighton.edu]
Dear List Members,

I was calculating intermolecular interaction energies using the
counterpoise method to correct the results for bsse (3 dimer centered
basis set calcs). The bsse contents were also calculated (2 more monomer
centered basis set calcs). If I'm not mistaken I can get the bsse
content if I subtract the non-bsse corrected energy from the bsse
corrected one. This imply that the bsse content should be positive.

I am using quite large basis set considering the investigated systems
(~50 atoms, cc-pVTZ, aug-cc-pVTZ) and the BSSE content is usually small,
less than 1kcal/mol; the interaction energies are in the 2-8 kcal/mol
range. The level of theory are lmp2 and dft.

However, in some cases (mainly lmp2 calcs) I got small negative (~
-0.3,-0.5 kcal/mol) bsse contents. 

Do you have any idea, how the bsse content can come to be negative?

Thanks, 
Jozsef


-- 
Jozsef Csontos, Ph.D.

Department of Biomedical Sciences
Creighton University,
Omaha, NE