Subject: Atomic Charges (GAMESS 93 vs. GAUSSIAN 92)!

From: [email-masked]
Date: Wed, 26 Jan 94 18:56:52 EST

Dear Alexandre,
 
     Sorry if this note is too brief or unclear (my car is illegally
parked, but I thought I'd check my mail!).  As far as I know, whenever
one performs any kind of calculation -- energy, charge distribution, etc. --
the calculation must be done on a molecule whose geometry has been
optimized WITH THE SAME BASIS SET.  Even two GAUSSIAN 92 runs, if they
are performed on molecules which were optimized using different basis
sets, but are, otherwise the same, will give two different answers.
I would think that even differences in the optimization between that of
GAMESS and that of GAUSSIAN 92 might affect this, too.  I hope this helps.
 
                                           Louis Grace
                                                  The University of Michigan
                                           Ann Arbor, MI   48109
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From: "Don H. Phillips" <[email-masked]>
Date: Thu, 27 Jan 1994 08:14:53 -0500

>Note that I used the same geometry in both calculations! And, in fact,
>the energy was practly the same! But the Mulliken charges...
>
>     Does it represent a bug in GAMESS 93?

>From the GAMESS REFS.DOC we see:
               An excellent review of the relationship between
          the atomic basis used, and the accuracy with which
          various molecular properties will be computed is:
          E.R.Davidson, D.Feller  Chem.Rev. 86, 681-696(1986).
 
          STO-NG      H-Ne        Ref. 1 and 2
                      Na-Ar,      Ref. 2 and 3 **
                      K,Ca,Ga-Kr  Ref. 4
                      Rb,Sr,In-Xe Ref. 5
...
...
..
          3) M.S.Gordon, M.D.Bjorke, F.J.Marsh, M.S.Korth
             J.Am.Chem.Soc. 100, 2670-2678(1978).
             ** the valence scale factors for Na-Cl are taken
                from this paper, rather than the "official"
                Pople values in Ref. 2.

So your Chlorine basis is not identical between the two calculations.
This probably explains the difference in you computed for the
(mythical) atomic charges.  
Don
l
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