> 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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Received on Mon Nov 14 2011 - 11:00:04 PST
