Subject: calculating atomic charges with AIMPAC

From: "Dr. Julia Metzker" <jm45|at|york.ac.uk>
Date: Thu, 29 May 2003 18:00:29 +0100

In reading the responses to my previous enquiry I decided I should probably 
include some more information.  The student working on this project has 
used G98 to generate the wavefunction file and is using the PROAIMV method 
of calculating the charges for methyl substituted benzenes and 
ferrocenes.  He has used an all electron basis  set in all of the 
calculation.  He has had success in all cases for benzene except hexamethyl 
benzene where he gets very large negative charges on some of the methyl 
carbons and methyl hydrogens.  I have looked at his wfn file and it indeed 
shows 45 doubly occupied molecular orbitals as expected.  I have also 
noticed that the N value (which I am assuming is the number of electrons 
associated with the atom) ranges from 6.5-7.5 for the atoms with large 
negative charges. and the L value is relatively large (10^-1 to `0 ^-2)  I 
have not yet tried the PROMEGA option.

I have two questions, really.

Can anyone tell me what the various information in the crt file means

and is there a simple way to figure out what is causing the very large charges?

The total charge does not add up to 0 as expected.  It is equal to -35.

I have included the relevant responses to my last email below

Thank you,
Julia Metzker

Dear Dr. Metzker,

It looks like you need to tightens the integration parameters in
"PROAIMV" and use the "PROMEGA" option (which seldom fails, but
slower of course) rather the usual option of "PROAIM" within the input
files (.inp).

To have an idea of the magnitudes of the charged on a Titanocene
moiety, perhaps you may wish to have a look at:

Bader RFW, Matta CF. Bonding to titanium. Inorg. Chem. 2001;40:5603-5611.

Best of luck,

Sincerely,

   Cherif

   -----------------------------------------
   Chirif F. Matta, Ph.D.
   Chemistry Department, University of Toronto,
   Toronto, Ontario, Canada M5S 3H6.
   Telephone:      (416) 978 - 3625
   Fax:            (416) 978 - 7580
   Web Site: http://chem.utoronto.ca/~cmatta/
   ------------------------------------------

I don't have any experience doing AIMPAC calcs, but I've read plenty of 
papers describing the calcs.

The charges on C seem unrealistic. The sum of the atomic charges must be 
the same as the molecular charge. If you have a neutral molecule that 
contains some highly negatively charged atoms, it must also contain some 
highly positively charged atoms. You didn't mention the latter, so I 
suspect that something was set up incorrectly.

Good luck,

-Alan

====
Alan Shusterman
Department of Chemistry
Reed College
Portland, OR

Hello,
Though I do not know which method you are using to get the wavefunction,
I would blame first to the quality of the wavefunction than to the aimpac
program. Check the boundaries of the carbon atoms to see if the atomic
basin is what you expect to be.
Hope it helps

_-_-_-_-_-_-_-_-_-_-_-_-

    Carlos Silva Lspez
  Dept. Qummica Organica
   Universidade de Vigo
   Phone:0034 986812226
-_-_-_-_-_-_-_-_-_-_-_-_

Hi,

   I just read your email on the CCL. My first question is what software are
you using to calculate the charges, proaimv, gaussian's implementation or
Kunig's AIM200?. The second question is how did you generate the wave
funcion, hf, dft, basis set. Best,

f

   Fernando Martmn,
      Plexxikon
      91 Bolivar Drive, Suite A
      Berkeley, CA 94710, USA
      510.647.4014 (phone)  510.548.8014 (fax)

Dear Julia,

These types of systems can be problematic if the topology of the density is
complex.  For example, are you certain that you've successfully identified the
ring and cage critical points in the ferrocene case (particularly) and assigned
them to the associated bond and ring critical points, 
respectively?  Problems in
this area can lead to the "overintegration" problems that you've described.

Curt Breneman
RPI Chemistry

--- You wrote:
The charges actually do not add to 0, indicating a problem somewhere, but I 
don't know where.
--- end of quote ---

This is definitely a problem if your molecules are neutral.

First, double-check the original wavefn/energy calculation. Perhaps the 
total charge was defined incorrectly.

Second, check your basis set. It is quite common to use effective core 
potentials (ECP) with organometallic compounds like ferrocene. If you used 
an ECP basis set, you have effectively deleted some or all of the core 
electrons from your wavefn. When you use this wavefn to calculate atomic 
charges you might get unrealistic results (but I would expect to see large 
*positive* charges due to the missing electrons, and not large negative 
charges).

Third, see if the wavefn and orbital occupancy info is being transferred 
correctly to AIMPAC. Perhaps AIMPAC thinks the wrong number of orbitals are 
populated?

Good luck,

-Alan

====

Alan Shusterman
Department of Chemistry
Reed College
3203 S.E. Woodstock Blvd.
Portland, OR 97202-8199
503-517-7699

   Dear Julia - have you checked the quality of the integrations? This is
usually best done with the number reported as "L" (I think the fourth
quantity output by proaimv). This is the value of the Laplacian integrated
over the atomic basin, which should vanish - values of 10^-3 are
borderline OK, lower is obviously better. Also check that the total
populations add up to the no. electrons in your system.

   For a system like ferrocene, with rings (and cages?), you might need to
tweak some of the surface-tracing paramaters - see the top of the
proaimv.f code.

   If this isn't the source of your problem, you could try the integration
methods in Gaussian (disappointing in my experience) or Popelier's
MORPHY, which is generally very robust.

   Hope this helps - Jamie