Hi all,
Just my two cents (although I suspect the exchange rate here is not equal
:P ), but a paper that might be interesting/relevant to the discussion is
Mobley, et al. J. Phys. Chem. B 2007, 111, 2242.
where they aimed to compare different charge fitting models, levels of
theory, and means of accounting for solvent polarization on the basis of
the explicit solvent solvation free energy of many small organic
compounds. The LJ terms were taken from GAFF I believe.
Importantly there were some significant mistakes in that work and a
clarification was recently published also:
J. Phys. Chem. B 2011, 115, 1329.
Brian
On Mon, Nov 14, 2011 at 1:36 PM, Ross Walker <ross.rosswalker.co.uk> wrote:
> > If we assume that both HF and MP2 provide an equally good [optimized]
> > geometries of the system (molecule), than the trick looks painless...
>
> The optimized structure, yes. But I would expect the actual electrostatic
> potential and thus the RESP fitted charges to come out different with MP2
> vs
> HF. The original choice of HF was because it underestimates the dipole
> moment in gas phase by approximately the same amount as the dipole moment
> changes when you solvate the molecule. This, I assume, will not be the case
> with MP2. Thus using MP2 is likely to have a fairly large effect on the
> electrostatic interactions outside of what the force field was
> parameterized
> for.
>
> FF03 changed the charge fitting scheme to include an implicit solvent term
> to generate solution phase charges from gas phase calculations instead of
> relying on the cancellation of errors that the HF approach uses. Hence
> improving the gas phase representation of the charges in the RESP fit does
> not necessarily correlate with better results for solution phase
> calculations.
>
> All the best
> Ross
>
> /\
> \/
> |\oss Walker
>
> ---------------------------------------------------------
> | Assistant Research Professor |
> | San Diego Supercomputer Center |
> | Adjunct Assistant Professor |
> | Dept. of Chemistry and Biochemistry |
> | University of California San Diego |
> | NVIDIA Fellow |
> | http://www.rosswalker.co.uk | http://www.wmd-lab.org/ |
> | Tel: +1 858 822 0854 | EMail:- ross.rosswalker.co.uk |
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>
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Brian Radak : BioMaPS
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Received on Mon Nov 14 2011 - 11:00:05 PST
