Subject: Fw: CCL:UFF

From: "derosa" <[email-masked]>
Date: Tue, 30 Oct 2001 21:22:38 -0500

Dear all:

I posted sometime ago a question on CCL about electronegativities on UFF.  I
got two answers and requests for summary.  Apparently there is not much
clarity about this, however I believe, the answers I got pretty much cover
the topic, besides solving my particular problem:-).  I will be interested
however if someone else follows this topic.  I'll send out to interested
people anything else I can found.

Thank you to Dr. Senn again, his thesis has all I (and probably anybody
else) needed about UFF, if you have a question about UFF you might want to
first take a look to sect. 2.7.3 in his thesis.
(full text at http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13972),
Sect. 2.7.3.

Thank you also to Dr. Bronwyn Thomas.  I actually looked for the paper he
pointed out but only electronegativity for a few atoms are shown sending the
reader to a reference submitted for publication, which, as happened to Dr.
Senn I could not find.  The electronegativity is however defined in the
paper pointed by Dr. Thomas and a full table of Generalized Pauling-Mulliken
electronegativities can be found in Dr. Senn Thesis.

Please see below the full answers and well at the bottom the original
question.

Thanks,

Pedro

***********************************************************************
Referring to your recent question sent to the CCL about the
electronegativities:
Another flaw of Rappé's paper; he refers to his "GMP
electronegativities" as submitted for publication, but the paper
never came out...

Back when I was doing it, Mark Thompson posted the same question to
the CCL (you should even be able to dig it out of the list archive).
He is the guy who wrote ArgusLab (http://www.planaria-software.com/),
which includes an UFF implementation. So I asked him to keep me
updated about the issue.
He finally got the GMP electronegativities directly from Rappé upon
request and forwarded them to me. That's why I referenced Table 2.2
in my thesis as personal communication from Rappé. At the time, Mark
told me that Rappé had told him he would put these values on the web.
Which never happened, I suppose...

Cheers,

Hans

*************************************************************************
These electronegativities are in eV. They have been calculated by Rappe and
Goddard - see J. Phys. Chem. 95, 3358-63 (1991), where some of these values
are reported. Nominally, they are calculated as the average of the
ionisation potential and the electron affinity (in eV).

However, some care should be taken when using these values, I have found.
Check that the quoted electronegativity does reflect the most recent values
of ionisation potential and electron affinity. Hydrogen is a bit of a
different case - see the paper mentioned above.

regards,
Bronwyn Thomas.

****************************************************************************
****************************************************************************
ORIGINAL QUESTION

> Dear all:
>
>         I have another question about Universal Force Field 1.02 as
> implemented in Cerius2.  Do any of you know which unit are used for the
> electronegativity?, According to Cerius they are in Pauling which is
> obviously not correct since several of them are larger than 4.  They seems
> to be in eV, for example UFF1.02 value for Li is 3.006 while according to
> one of my references (Density-Functional Theory of Atoms and Molecules, by
> Parr and Yang) this value is 3.01 which is given in eV.
>
> Other values agree fairly well, F(UFF1.02)=10.874 vs. F(Parr)=10.41 eV.
>
> But other values are awfully different like for example H(UFF1.02)=4.528,
> H(Parr)=7.18 eV, or Cu(UFF1.02)=3.729 while Cu(Parr)=4.48 eV.
>
> Is this different due to a parameterization obtain in different experiment
> or they are really given in a different unit.
>
> Thank you for your help
>
> Pedro
>