Hi
Without sending use the actual inputs for RESP
it is difficult to say what can be wrong with the 1. - the RESP usage.
As far as point 2.- this type of behavior is observed in some other cases
and this - we don't fully understand yet.
Piotr
On Mon, 5 Dec 2005, Carlos Jaime wrote:
> Date: Mon, 05 Dec 2005 18:43:16 +0100
> From: Carlos Jaime <carlos.jaime.uab.es>
> Reply-To: amber.scripps.edu
> To: amber <amber.scripps.edu>
> Subject: AMBER: RESP: Question
>
> Dear all,
> Our group is using Amber since long ago. Nowadays we are sistematically using
> Amber v.7, and one of my Ph.D student face with one problem with RESP that I
> want to expose.
> We are using RESP to get a set of atomic charges that are 'independent from
> the conformation' of the substrate. We usually compute several conformations
> with an ab initio program (usually Gaussian), get the structure and energies,
> and we use the structure, the energy and the atomic charges into RESP, with
> the multiconformer option, to get an unique set of atomic charges.
> When working with fluorine compunds, we realized that averaging two
> conformers, the fluorine atoms got a charge almost zero. We checked the
> behaviour of the RESP program with individual conformations and is working
> properly, but as soon as we are using more than one conformer, the charges
> are greatly reduced and several values are finally near zero.
> We were really surprised and we started to search through the RESP code. We
> found thet RESP do not average charges but average the molecular
> electrostatic potentials. This means that the average of the meps of two
> conformers that are enantiomeric is almost null, and atomic charges are then
> also almost zero.
>
> Finally we end up with two possibilities:
> 1.- we are using RESP in a wrong way
> 2.- something in RESP is not properly working
>
> Has anyone faced with this problem before?
> Can someone give us some information about this point?
>
> Thanks in advance.
>
> --
> Carlos JAIME
> Dept. Quimica, Fac. Ciencias (Cn)
> Univ.Autonoma Barcelona
> 08193 Bellaterra (Barcelona), SPAIN
> Phone: ++34-935812591
> Fax: ++34-935811265 or ++34-935812477
>
>
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Received on Mon Dec 05 2005 - 18:53:01 PST
