The calculation of partial charges for optimal reproduction of the
electrostatic potential around a molecule is only deterministic in the
limit of an agreed upon figure of merit, a perfectly consistent method, and
an identical data set. In your case, the data set is a series of
points scattered around the molecule, as selected by either program, and
the figure of merit is a least squares optimum given hyperbolic restraint
equations. The two programs may not even perform that in precisely the
same way, but I suspect that the root of your problem is the selection of
the points at which to take the electrostatic potential for composing the
fitting matrix. A better analysis is to take the partial charges coming
from each program, select a set of your own points around the molecule
where you think water or other matter might experience their electrostatic
potential, and then calculate the charge models' projected electrostatics
at those points. See how well those agree, and if the difference is still
large then come back and we'll look at it some more.
Dave
On Thu, Nov 26, 2020 at 12:54 PM Michele Vanini <
michele.vanini.student.kuleuven.be> wrote:
> Dear all,
>
> I have a question regarding the partial charges calculation for a GAFF
> parametrization.
>
>
> I have calculated them with two methods
>
> GAUSSIAN+ resp (antechamber)
>
> GAMESS US + resp
>
>
> Using the same molecule, the same level, HF 6-31G I obtain different
> values.
>
>
> Do you know how to fix this problem?
>
> If you prefer I can put all the input commands.
>
>
> Regards
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>
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Received on Thu Nov 26 2020 - 18:30:03 PST
