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Related Concept Videos

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
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Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
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¹H NMR: Long-Range Coupling01:27

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Spatial Separation of Molecular Conformers and Clusters
10:37

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Published on: January 9, 2014

Coupled-cluster dynamic polarizabilities including triple excitations.

Jeff R Hammond1, Wibe A de Jong, Karol Kowalski

  • 1Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA.

The Journal of Chemical Physics
|June 17, 2008
PubMed
Summary

Accurate dynamic polarizabilities for molecules were calculated using coupled-cluster linear response theory. Results show that advanced methods like CCSDT-LR and CC3 provide reliable data, especially for systems with dynamic correlation.

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Area of Science:

  • Quantum Chemistry
  • Computational Chemistry
  • Molecular Properties

Background:

  • Coupled-cluster (CC) theory is a powerful method for calculating molecular properties.
  • Linear response theory is essential for determining dynamic polarizabilities.
  • Accurate calculations are crucial for understanding molecular behavior in external fields.

Purpose of the Study:

  • To compute dynamic polarizabilities for open- and closed-shell molecules.
  • To evaluate the performance of various approximate CC methods.
  • To assess the impact of electron correlation and reference choice on accuracy.

Main Methods:

  • Coupled-cluster (CC) linear response theory with full singles, doubles, and triples (CCSDT-LR).
  • Utilized large basis sets and the NWChem software suite.
  • Employed four approximate CC methods with augmented cc-pVNZ basis sets.

Main Results:

  • CCSDT-LR and CC3 methods yield nearly identical results for systems dominated by dynamic correlation.
  • CC3 overestimates triples contributions in cases of significant static correlation.
  • The choice of reference (ROHF vs. UHF) significantly affects open-shell polarizability accuracy.

Conclusions:

  • Advanced CC methods, particularly CCSDT-LR, provide accurate dynamic polarizabilities.
  • Extrapolation techniques using high-level CC calculations can effectively reproduce experimental data.
  • Understanding correlation effects and reference choice is vital for accurate open-shell calculations.