Interrelations between the a priori and a posteriori BSSE correction schemes

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The a priori BSSE-free chemical Hamiltonian approach (CHA) of computing intermolecular interaction energies usually gives results dose to those obtained by the a posteriori counterpoise (CP) basis set superposition error (BSSE) correction scheme of Boys and Bernardi. As the basis set improves, the difference between the results of these BSSE-corrected methods diminishes much faster than BSSE disappears from the uncorrected interaction energies. Here we try to give a possible explanation of this behavior, by considering two different aspects of interrelations between the two schemes. We present a formal perturbation-theoretical analysis indicating that the behavior can be rationalized on the basis of observing that BSSE and true intermolecular interactions can be considered additive effects under certain conditions, providing formal justification for the tacit additivity assumption inherent in the CP formalism. We also present an analysis of the alternative interpretations of the CP scheme, which allows one to define the CP-corrected density matrix, permitting calculation of CP-corrected quantities for electron density and bond orders. Diagonalizing the CP-corrected density matrix, one can arrive at one-electron orbitals, the use of which gives energies dose to the CHA-SCF ones. The results indicate that the two conceptually different BSSE correction schemes corroborate each other not only in the sense of giving dose numerical results but also at the level of the theoretical analysis.

Original languageEnglish
Pages (from-to)559-566
Number of pages8
JournalInternational Journal of Quantum Chemistry
Issue number4 SPEC. ISS.
Publication statusPublished - Nov 15 2004



  • BSSE
  • BSSE correction (a priori and a posteriori)
  • Basis set superposition error
  • Chemical hamiltonian approach
  • Counterpoise correction

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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