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Difficulties of density functional theory in predicting the torsional potential of 2,2′-bithiophene

✍ Scribed by Pedro M. Viruela; Rafael Viruela; Enrique Orti

Publisher
John Wiley and Sons
Year
1998
Tongue
English
Weight
212 KB
Volume
70
Category
Article
ISSN
0020-7608

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✦ Synopsis

The internal rotation of 2,2Ј-bithiophene was investigated within the Ž . density functional theory DFT approach. Fully optimized DFT torsional potentials are Ž . compared with Møller᎐Plesset MP2 results which predict a fourfold potential with s-cis-and s-trans-gauche minima. DFT calculations fail in describing the energetics of the internal rotation because they favor planar vs. perpendicular conformers. Gradientcorrected functionals provide torsional potentials where the gauche minima have almost vanished and the s-cis l s-trans interconversion barriers are twice as high as the barriers obtained at the MP2 level. The use of local functionals augments the shortcomings of the DFT approach. The gauche minima completely disappear and the rotational barriers are now about three times higher than the MP2 barriers. As an efficient computational approach, we suggest having geometries optimized at the DFT level and conformational energies evaluated via single-point MP2 calculations. The fitting of MP2rrDFT energies to truncated Fourier expansions allows one to predict the torsional angles and the relative energies of the critical points of the rotational potential with an accuracy similar to that afforded by MP2 calculations including full geometry optimization.

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