AMBER Archive (2004)

Subject: Re: AMBER: RESP vs. AM1-BCC charges for isoprene

From: Carsten Detering (detering_at_u.washington.edu)
Date: Fri Jul 16 2004 - 16:33:51 CDT

Olli,

kann es sein, dass die Polarisierung auf den Wasserstoffen mit '+' einen
Unterschied gemacht haette? So hast Du ja nur Polarisierung auf den
Schweratomen.

Ist nur so ein Gedanke...

Carsten

Oliver Hucke wrote:

> Dear Amber users,
>
> I have derived partial charges for an isoprene moiety with AM1-BCC and
> with the resp procedure. I was surprised by the big differences of some
> charge values - as you can see in this sketch:
>
> AM1-BCC RESP
>
> H3 0.04 H3 0.10
> | |
> C -0.06 H 0.11 C -0.36 H 0.09
> \ / \ /
> -0.12 C=====C -0.17 0.2 C=====C -0.26
> / \ / \
> C C -0.06 C C -0.24
> | | | |
> H3 H3 0.04 H3 H3 0.09
>
> Especially the carbons engaged in the double bond look suspicious to me
> in the resp output (change of one charge from -0.12 with am1-bcc to 0.2
> with resp). Might this be a resp fit artefact?
>
> My understanding was is the AM1-BCC method was designed to reproduce the
> RESP charges. So, I am wondering if something went wrong here.
>
> Your comments are highly appreciated.
>
> Oliver
>
> =====================================
> Details of what I did are given here:
>
> AM1-BCC:
>
> antechamber -fi pdb -i isopren.pdb -fo mol2 -o isopren.mol2 -c bcc
>
> RESP:
>
> 1. Geometry optimization with gaussian98:
> # HF/6-31G* opt scf=tight test
> 2. ESP calculation:
> # HF/6-31G* pop=mk iop(6/33=2) iop(6/42=6) geom=check
>
> Then:
>
> antechamber -fi gout -i isopren.out -fo ac -o isopren.ac
> espgen -i isopren.out -o isopren.esp
> respgen -i isopren.ac -o isopren.respin1 -f resp1
> respgen -i isopren.ac -o isopren.respin2 -f resp2
> resp -O -i isopren.respin1 -o isopren.respout1 -e isopren.esp \
> -t iso.qout1
> resp -O -i isopren.respin2 -o isopren.respout2 -e isopren.esp \
> -q iso.qout1 -t iso.qout2
>
>
>
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