Let's make sure we all understand what these torsional potentials mean.
They are NOT the true torsional potential that the system feels if
computed under the 'perfect force field' or a great QM hamiltonian.
They are in fact, a fudge factor introduced to correct for imperfections
in the force field.
So, there WILL be a barrier even if the torsional potential has a zero
force constant.
Now, is this barrier good enough, and are the minima in the correct
place? To answer that you must do a torsional potential scan with a good
QM method, and compare that energy profile with what the force gives you
with a 'zero' torsional potential.
The difference between those two calculations in then fit with a fourier
series. Voila, you got your tosional potential then.
a.
Chih-Ying Lin wrote:
>
> Hi
> I found that the dihedral CCNN force field for the azobenzene are not quite right.
> 0 3.14 3.0 :1.CAH :1.CAM :1.NAK :1.NAL (9,11,12,13)
>
> With this set of parameters, the two phenl rings can rotate freely.
> Any one have idea for this?
>
> Thanks
> Lin
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--
Dr. Adrian E. Roitberg
Associate Professor
Quantum Theory Project and Department of Chemistry
University of Florida PHONE 352 392-6972
P.O. Box 118435 FAX 352 392-8722
Gainesville, FL 32611-8435 Email adrian.qtp.ufl.edu
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Received on Sun Apr 27 2008 - 06:08:18 PDT
