AMBER Archive (2002)

Subject: Re: Antechamber generating bad charges w/ gaussian 98.

From: James W. Caldwell (caldwell_at_heimdal.compchem.ucsf.edu)
Date: Wed Oct 23 2002 - 18:16:05 CDT

What do the intermediate files look like? Especially what are the
ESP charges from your gaussian run? They should be similar.

jim

On Wed, 23 Oct 2002, Nicholson, James D Mr ARO wrote:

>
>All:
>
>
>I am trying to generate charges for a modified nucleic base using
>Antechamber and the RESP protocol. However, the charges are highly
>exagerated. In many cases the charges are have changed sign from what is
>found in the corresponding parm98 unit or in the mopac calculation for the
>same molecule.
>
>I'm getting methyl hydrogens having partial charges of -2.51!
>
>Here are the steps I used to create this mess:
>1) Created model in insight
>2) Minimized using mopac interface in insight environment
>3) "antechamber -i <input file> -fi mol2 -o <output> -fo gcrt"
>4) Edited the output of antechamber to only run optimization, since, I was
>having problems w/ Gaussian crashing. I basically ran the input through a
>Gaussian (g98) minimization by changing the first link to:
> UHF/6-31G* Test opt SCFCYC=256
>5) Took the optimized output and ran a single point resp calculation with
>first link being:
> UHF/6-31G* Test SCF=Tight Pop=MK iop(6/33=2) iop(6/42=6)
>
>which is basically the antechamber-generated file w/o the optimization.
>
>6) Calculated charge w/ the following command.
> antechamber -i <gaussian .out> -fi -gout -o <prep file> -fo -prepi
>-c resp
>
>7) Examined the prep file w/ xleap to discover the bad charges.
>
>
>The problems seem to be most pronounced along a stretch of extended alkyl
>chain. I remember in some of the papers that this can be a problem.
>However, there are problems all over.
>
>Could this be a units mismatch between Gaussian and amber? Gaussian is
>working in Hartree-Bohr-Radians. I doubt it, but, need to mention it as a
>possibility.
> 

-- 

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