## Abstract

In order to include the effects of electron correlation in ab initio molecular orbital calculations it is necessary to go beyond the single determinant Hartree-Fock (BF) level of theory. In the present investigation the influences of both dynamic and nondynamic correlation effects on the optimised geometries and F-19 nuclear shielding calculations of the twelve fluorobenzenes are reported. The non-dynamic electron correlation effects are represented by complete-active space self-consistent field (CASSCF) calculations. Second- and fourth-order Moller-Plesset (MP2 and MP4) calculations are used to describe the dynamic electron correlation effects, Some density-functional (DFT) results are also reported which do not distinguish between dynamic and non-dynamic electron correlation. Following the correlated geometry optimisations 19F nuclear shielding calculations were performed using the gauge-included atomic orbitals (GIAO) procedure, these were undertaken with wavefunctions which include various levels of electron correlation including HF, CASSCF and MP2. For the calculations of the optimised geometries, and some of the nuclear shieldings the 6-31G** basis set is used whereas the locally-dense [6-31G** on C and Il and G-311++G(2d,2p) on F] set is used for some of the shielding calculations. A comparison of the results of HF shielding calculations using other basis sets is included. Comparison of the calculated geometry and shielding results with relevant, reported, experimental data is made.

Original language | English |
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Pages (from-to) | 101-112 |

Number of pages | 12 |

Journal | BULLETIN OF THE POLISH ACADEMY OF SCIENCES-CHEMISTRY |

Volume | 48 |

Issue number | 1 |

Publication status | Published - 2000 |

## Keywords

- electron correlation effects
- geometry optimisation
- F-19 nuclear shieldings
- fluorobenzenes
- ab initio molecular orbital calculations
- locally-dense basis set
- RESONANCE CHEMICAL-SHIFTS
- PERTURBATION-THEORY
- ATOMIC ORBITALS
- NUCLEAR
- CONSTANTS
- TENSORS
- MOLECULES