AMBER Archive (2007)

Subject: Re: AMBER: CONFIGURATION FILE FOR OXALATE C2O4^2-

From: Jiri Sponer (sponer_at_ncbr.chemi.muni.cz)
Date: Tue Sep 18 2007 - 03:11:19 CDT

I agree with Ilyas:

Mulliken charges are essentially useless, being extremely
method and basis set dependent. (Changing marginally one of the inner
s basis function exponent on Mg2+ (fully hydrated and bound to a ligand)
can change the calculated Mulliken value on Mg by 0.3 e, despite that
this change of AO does not change any real property of the system
by even 0.001 %....

You can use constraints, if you need to impose some geometry
restrictions. Gaussian is however the best code for geometry optimizations.

Jiri

s orbital exponent on Mg2+
> Dear Eduardo,
>
> I wonder why you wanted to get the Mulliken charges. Did you try to follow
> the resp protocol to get the RESP charges?
>
> On Mon, 17 Sep 2007, Eduardo Mendez wrote:
>
> > As Shakespeare said sometime in a dream of mine"Whats on an
> > approximation, whatever else its basis set it would smell as sweet (he
> > may have said that about aromatic compounds)"
> >
> > I tried a different program and got Mulliken charges, the question
> > however remains open, as
> > I do not know to what degree my calculations will be accurate. If anyone
> > knows something about
> > the mischievous Oxalate let me know.
> >
> > Eduardo
> > Eduardo Mendez wrote:
> > > Greetings Amber users
> > >
> > > I was wondering if anyone could share the amber parameter files for
> > > oxalate. I did gaussian calculations to get the mulliken charges,
> > > however, to my dismay, gaussian gives me an isomer, which
> > > is not in the planar conformation one would expect it to be :(
> > > Any idea were can I find a library site other than
> > > http://pharmacy.man.ac.uk/amber/ ???
> > >
> > > Thanks in advance
> > >
> > > eduardo
> > > -----------------------------------------------------------------------
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>
> --
> Ilyas Yildirim
> ---------------------------------------------------------------
> = Department of Chemistry - =
> = University of Rochester - =
> = Rochester, NY 14627-0216 - Ph.:(585) 275 67 66 (Office) =
> = http://www.pas.rochester.edu/~yildirim/ =
> ---------------------------------------------------------------
>
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