Subject: DFT/ BSSE question

From: "Tapas Kar" <[email-masked]>
Date: Mon, 5 Mar 2001 17:25:09 -0700

Hi,
For c2h2 + H+ = C2h3+,  dft(b3lyp) bsse complexation energies (DE=Ecomp-E(c2h2)) using 6-31g, 6-31G*, 6-311G**,
6-311++G**, 6-311++G(3df,3pd) and aug-cc-pVTZ basis set are slightly higher than non-bsse energies.
For example: DE = -157.51 kcal/mol (without BSSE) and -158.21kcal/mol (with BSSE); B3LYP/6-311++G** results.
However MP2 shows correct trend of lowering bsse complextion energies with such basis functions.
DE = --156.15 kcal/mol (without BSSE) and -153.90 kcal/mol (with BSSE); B3LYP/6-311++G** results
What's wrong with b3lyp bsse.  Why B3LYP energy of c2h2 (-77.35637) at the geometry of C2h3+ and with excess basis
function of H is higher than the energy of C2h2 (-77.35748) at its own geometry?
Thanks,
Tapas
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Tapas Kar, Ph. D
Department of Chemistry & Biochemistry
Utah State University
Logan, UT 84322-0300

Tel: 435-797-7230
Fax: 435-797-3390
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