[gmx-users] question about torsional potential fitting

[Victor Rosas Garcia]

Excellent!

Thanks a lot André

2014-10-08 14:41 GMT-05:00 André Farias de Moura <moura at ufscar.br>:
> There is no such thing as absolute energies and you may safely set the
> minimum energy in your profile to zero.
> (parallel profiles are the same profile when it comes to compute forces,
> for instance, since the constant term yields a null derivative)
>
> best
>
> Andre
>
> On Wed, Oct 8, 2014 at 3:50 PM, Victor Rosas Garcia <rosas.victor at gmail.com>
> wrote:
>
>> Hello everybody,
>>
>> I have calculated ab initio energies for a torsional potential that I
>> want to fit to a Fourier series. I have calculated the difference
>> between the ab initio energies and the forcefield with the torsion
>> potential set to zero (lets call that "diff curve").  This gives me a
>> somewhat jagged periodic function. I can then get a cosine series that
>> parallels the shape of the diff curve, but it is displaced along the
>> energy axis.
>> see this plot
>>
>>
>> https://drive.google.com/file/d/0B2K7fedV_ZFzM3hXZVhyS2VvYnM/view?usp=sharing
>>
>> If I shift the plot of the series, by adding a constant term, the fit
>> doesn't look so bad, to me at least, as in the following plot
>>
>>
>> https://drive.google.com/file/d/0B2K7fedV_ZFzRmlpcnZhckEtdUE/view?usp=sharing
>>
>> However, I cannot add that constant term in the itp file for my
>> molecule. Is it enough if the energies calculated by the Fourier
>> series are parallel to the diff curve?
>>
>> Best regards
>>
>> Victor
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>
>
> --
> _____________
>
> Prof. Dr. André Farias de Moura
> Department of Chemistry
> Federal University of São Carlos
> São Carlos - Brazil
> phone: +55-16-3351-8090
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