CCL: negative bsse content

 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