While it is certainly true that CCl4 is not polar, and doesnt have dipole or
quadrupole
moments (it does have an octopole moment of 26.1x 10^(-34) esu cm^3) my
feeling
is that all charges equal 0 is more a problem with your resp fitting than an
underlying
characteristic of CCl4...so I went back and checked my lab journals (I was
fiddling
around with CCl4 a couple of years ago) and thats what I found:
basis set q(C) q(Cl)
6-31G* -0.388 0.097
6-31G(3df,2p) -0.5398 0.1350
6-311++G(3df,2p) -0.5091 0.1273
So the carbon actually has a considerable charge which is then balanced by
the
chlorines...and despite chemical intuition, its the chlorines which are
positively
charged...
Besides that, Im not sure why you do a two-stage fit anyways...
Th.
Dr. Thomas Fox
Dept. Chemical Reseach / Structural Research
J51-00-01
Boehringer Ingelheim Pharma KG
88397 Biberach/Germany
Thomas.Fox_at_bc.boehringer-ingelheim.com
> -----Original Message-----
> From: jim caldwell [SMTP:caldwell_at_heimdal.compchem.ucsf.edu]
> Sent: Friday, June 22, 2001 23:03
> To: Jones de Andrade
> Cc: Jones de Andrade; amber_at_heimdal.compchem.ucsf.edu
> Subject: Re: CCl4 charge problem...
>
>
> Well, depending on the basis set you are using it doesn't
> seem unreasonable that you could come out with all 0's.
> There's nothing a priori wrong with that result...CCl4 IS
> a non-polar solvent :-)
>
> On Fri, 22 Jun 2001, Jones de Andrade wrote:
>
> > Hello all!
> >
> > Just a question: Have anybody here any day seen anything like a
> > zero charge in carbon, when calculating the charges of, for example,
> CCl4?
> >
> > I'm gotting it in the first resp stage, so, when I try to
> > constrain the chlorine atoms in the second stage, all then become 0!
> Since
> > this calculations have already been done and published, I'm just trying
> to
> > reproduce those results before starting to calculate the charges for my
> > mastering thesis simulations.
> >
> > Moreover, if it can help: I'm using the script available at the
> > amber site to obtain the data from the .dat file generated by gamess
> > program with 6-31G* level of theory.
> >
> > Any suggestion will be very welcome.
> >
> > Thanking you all, and apologizing myself for taking your time,
> >
> > Sincerally yours,
> >
> > Jones de Andrade
> >
> > ***********************************************************
> > * Jones de Andrade *
> > ***********************************************************
> > * Theoretical Chemistry Group * Grupo de Quimica Teorica *
> > * http://www.iq.ufrgs.br/theochem.html *
> > * Institute of Chemistry * Instituto de Quimica *
> > * http://www.iq.ufrgs.br/ *
> > * Universidade Federal do Rio Grande do Sul *
> > * http://www.ufrgs.br/ *
> > * Brasil *
> > ***********************************************************
> > * E-mail:johannes_at_iq.ufrgs.br *
> > * ICQ UIN: 17929775 *
> > ***********************************************************
> > * "We turn molecules into numbers, *
> > * and numbers into molecules..." *
> > ***********************************************************
> >
> >
> >
> >
>
>
> --------------------------------------------------------------------------
> --
> James W. Caldwell (voice) 415-476-8603
> Department of Pharmaceutical Chemistry (fax) 415-502-1411
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Received on Wed Jun 27 2001 - 01:16:19 PDT
