RESP charge derivation

From: Lepsa <>
Date: Tue 4 Feb 2003 18:34:57 +0100

Dear AMBER commmunity,
I'm not quite sure what's the proper way to derive charges by RESP on ligand
for ff99.

1) Do I need to minimize the structure (or hydrogens?) What level of theory?
(in this case I have an x-ray stucture of the inhibitor complexed with
receptor; I add hydrogens in INSIGHT II)

2)As James Caldwell wrote:
#HF/6-31G* SCF=tight Test Pop=MK iop(6/33=2) iop(6/42=6) opt

Is the tight convergence crucial (or better)? How much?

>>>>>iop(6/42=6) calculate 6 points per unit area for the ESP, default is 1
(I have no idea what the unit area
                                                    actually is)

Is this iop necessary? I hadn't seen this before........

Is multiple-conformation charge-fitting recommended? (generally or for my
case?) How many conformations do I need? How do I geneate them?

Thanks for your answers.

All the best,



Martin Lepsik, PhD student            Phone:  +420/2/20183-540, Fax:
Dept. of Theor Chem & Center for Complex molecular Systems and Biomolecules
Institute of Organic Chemistry and Biochemistry (IOCB)
Flemingovo nam 2,
Czech Academy of Sciences,
166 10, Prague 6,
Czech Rep.
Received on Tue Feb 04 2003 - 09:34:57 PST
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