AMBER Archive (2003)

Subject: AMBER: charge fitting

From: Itziar Maestre Asenjo (itziar_at_qorws1.uab.es)
Date: Tue Nov 25 2003 - 02:28:05 CST

Dear amber users

I am trying to calculate the charges for one organic molecule wich looks
like this:

                                          H H
                                          | |
                O H O C = C
                || | | / \
H-O(*)-C-C-N-S-C C-H
                     | | \\ //
                    H O C - C CH3
                                       / \ /
                                H-C C-N
                                      \\ // \
                                        C - C CH3
                                         | |
                                        H H

I am using the RESP metodology with 5 different conformations. I make
charge restriction for the H in the carboxilic group, and I set multiple
molecule atom equivalencing
for the rest of the molecule atoms .

I find that the charge on the O(*) of the carboxilic group is extremely
low ( -0.086) compared to that obtained with DFT calculations (-0.732)
and with that one obtained with antechamber for a single conformation (
(-0.683)

Can someone explain me why I get such a small charge when I use the RESP
metodology?
And is there any way to use different conformations to create the
file.prep with antechamber in a similar way that it is done using the
RESP metodology?

Thanks in advance

Itzi

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