### Abstract

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 language | English |
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Pages (from-to) | 145-152 |

Number of pages | 8 |

Journal | Journal of Molecular Structure |

Volume | 141 |

Issue number | C |

DOIs | |

Publication status | Published - 1986 |

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### ASJC Scopus subject areas

- Structural Biology
- Organic Chemistry
- Physical and Theoretical Chemistry
- Spectroscopy
- Materials Science (miscellaneous)
- Atomic and Molecular Physics, and Optics

### Cite this

*Journal of Molecular Structure*,

*141*(C), 145-152. https://doi.org/10.1016/0022-2860(86)80318-0

**Quantum chemical calculation of force constants and vibrational spectra.** / Fogarasi, G.; Pulay, P.

Research output: Article

*Journal of Molecular Structure*, vol. 141, no. C, pp. 145-152. https://doi.org/10.1016/0022-2860(86)80318-0

}

TY - JOUR

T1 - Quantum chemical calculation of force constants and vibrational spectra

AU - Fogarasi, G.

AU - Pulay, P.

PY - 1986

Y1 - 1986

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=0041139000&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0041139000&partnerID=8YFLogxK

U2 - 10.1016/0022-2860(86)80318-0

DO - 10.1016/0022-2860(86)80318-0

M3 - Article

AN - SCOPUS:0041139000

VL - 141

SP - 145

EP - 152

JO - Journal of Molecular Structure

JF - Journal of Molecular Structure

SN - 0022-2860

IS - C

ER -