sanya
sanya@photonics.ru
On Wed Oct 3 '12 12:25pm, Alexey Nikitin wrote
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>Hi all
>I had a problem with the calculation of the torsion potential in the molecule FOOF.
>When rotating the torsion angle two strange effects observed:
>1. F-O bond length is changed up to 0.2 A
>2. The energy barrier of rotation differs by almost 100 kcal / mol (!!!), depending on the method: HF, MP2, MP3, MP4. Moreover MP3 worse than MP2.
>(I used the basis sets: 6-311+G(2d,p), cc-pVDZ and cc-pVQZ)
>Could you be so kind to explain what the problem is and how to overcome it?
>And more general question. I still considering the calculation of torsion angles in the cc-pVQZ MP2 as a very robust procedure. When it does not work?
>