BSSE-free SCF theories:: a comment

Some aspects of creating the basis set superposition error (BSSE) problem at the SCF level are briefly discussed. It is stressed that - contrary to the recurring propositions in the literature - the BSSE-problem cannot be properly handled by restricting each molecular orbital to be expanded in the basis of only one of the monomers, because this also excludes the physically important, true charge-transfer effects. The discussion is illustrated by some calculations performed for water dimer and for two pairs of nucleic bases (thymine-adenine and uracil-adenine) which are compared with those in the recent paper of Gianinetti et al. [E. Gianinetti, M. Raimondi, E. Tornaghi, Int. J. Quant. Chem. 60 (1996) 157]. (C) 2000 Elsevier Science B.V. All rights reserved.