Quantum chemical calculation of force constants and vibrational spectra

G. Fogarasi, P. Pulay

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As a result of the development of direct derivative methods and improved computational facilities, ab initio quantum chemical calculations have become an increasingly important source of information for the determination of molecular force constants. Within the Hartree-Fock (H-F) SCF model and using moderate size basis sets such calculations are now economically feasible for molecules of up to 2o-3o atoms. At this level of theory, harmonic diagonal force constants are overestimated by 1o-3o%, corresponding to 5-15% in the frequencies. However, the largely systematic errors can be accounted for by simple empirical corrections. The resulting SQM (Scaled Quantum Mechanical) force fields are probably the most reliable ones available at present for larger molecules. Calculated infrared intensities are semi-quantitatively correct. Beyond the H-F model, large scale calculations including electron correlation give great improvements in the force constants, but there are still residual errors of a few percent.

Original languageEnglish
Pages (from-to)145-152
Number of pages8
JournalJournal of Molecular Structure
Issue numberC
Publication statusPublished - Mar 1986


ASJC Scopus subject areas

  • Analytical Chemistry
  • Spectroscopy
  • Organic Chemistry
  • Inorganic Chemistry

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