CCL: negative bsse content



 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