Hi,
The antechamber "automated way" to determine RESP charges, as reported
here: http://www.ub.edu/cbdd/?q=content/gaussian-09-and-antechamber12 ;
create gaussian input files with the following keywords: iop(6/33=2)
iop(6/42=6) iop(6/50=1).
But it seems that using iop(6/50=1) only is a better way to get well
balanced charges for the amber & gaff forcefields.For example, only this
keyword is mentionned In the gaussian manual (
http://www.gaussian.com/g_tech/g_ur/k_population.htm ).
Why are those extra keywords iop(6/33=2) & iop(6/42=6) added in
the automated way?
*Jérémie Knoops*
*PhD StudentLaboratory for Chemistry of Novel Materials
<
http://morris.umh.ac.be/default.aspx>*
*University of Mons* <
http://portail.umons.ac.be/en2/>
2015-10-27 11:02 GMT+01:00 Ye Mei <ymei.itcs.ecnu.edu.cn>:
> RESP charge fitting suffers from ill-conditioning of the linear equations,
> which means that you may get "degenerate" solutions for the atomic charges.
> Some might be unphysical.
> Usually, AM1 charges are fine. Or I should say they are compatible with
> existing AMBER force fields.
> If you REALLY want to use ESP-based charge, you can use our dRESP charge
> fitting method ( doi: 10.1002/jcc.23208) taking AM1 charge as an initial
> guess.
> Or you can hack the resp code by replacing LU decomposition with SVD
> analysis and setting the null space to zero.
>
> Good luck,
>
> Ye
>
> On 10/27/2015 04:38 PM, Jérémie Knoops wrote:
> > Dear Amber users,
> >
> > I'm trying to determine the charges for phenylguanidinium.
> > I normally use the RED servers (and very often multiconfigurational fit)
> > but the q4md website is still down.
> > Using RESP and Gaussian with one conformation (minimized structure), I
> get
> > too high absolute values for them (up to 1.1 for a carbon atom,
> > see GdPhenyl_resp.mol2).
> > It's impossible to parametrize the molecule with those charges, the
> > equilibrium bond length is 0.06 Å shorter than the reference bond length.
> >
> > I tried the am1-bcc scheme, also with one conformation and the charges
> > seem reliable (see GdPhenyl_am1-bcc.mol2). I can parametrize the torsion
> > with them.
> > Do I have to use the am1-bcc charges? Are they really reliable? Are there
> > other options?
> >
> > Thank you for your advice.
> >
> > *Jérémie Knoops*
> >
> > *PhD StudentLaboratory for Chemistry of Novel Materials
> > <http://morris.umh.ac.be/default.aspx>*
> > *University of Mons* <http://portail.umons.ac.be/en2/>
> >
> >
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>
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Received on Mon Nov 02 2015 - 01:30:04 PST
