Anatoly,
I did not consider magic numbers & don't know for certain what the
exact # is. The 95 atom cluster is only an estimate of the size of the
composition of particles that was observed in TEM images of Pt tethered
onto a a surface with -COH, -C=O groups; the exact nature of the bonding
is what I'm trying to determine. The Pt seems to be stabilized by its
surface interactions; the exact nature of the binding is what I'm trying
to figure out. The EXAFS data that I have "sees" both the Pt-Pt
interactions as well as the Pt-surface interactions. I realize that
it would be best to simple scan a sample containing Pt clusters of the
same size as observed in the TEM; but, unfortunately, Pt has a tendency
to agglomerate and it is difficult to get a monodispersed size in
colloidal suspension in solution. Comparing with Pt foil doesn't
work because of the quenching problems in the fluorescence since there
are so many atoms.
I wanted to get a simulated EXAFS spectrum of something that just
represents the bulk Pt-Pt only to compare with the data that I
have. Differences in the spectra (in principle) would be attributed
to Pt-surface interactions present in the TEM. I would like to try
to get an idea of the # of Pt interacting with the surface as opposed to
the Pt-Pt interactions.
Charles
At 09:23 PM 5/16/2005, you wrote:
Charles,
The 95 atoms Pt cluster you describe sounds
strange. It does not fit any sequence of magic numbers typical for
regular polyhedral clusters (13, 55, 147... for cuboctahedral fcc and
icosahedral clusters, or 13, 38, 79, 140... for truncated
octahedral or : 10, 37, 92, 185...for supported cuboctahedral
clusters).
If you are modeling an fcc cluster (Pt does
pack into fcc structure, even for sizes smaller than your clusters,
contrary, e.g., to Au which is possible to observer in icosahedral
structure for 13-atom clusters) then your "spherical" cluster
of 95 atoms is not a closed shell cluster and thus it is not a stable
isomer. What are you trying to accomplish?
Anatoly
Anatoly Frenkel
- -----Original Message-----
- From: ifeffit-bounces@millenia.cars.aps.anl.gov
[
mailto:ifeffit-bounces@millenia.cars.aps.anl.gov]On Behalf Of
Charles Chusuei
- Sent: Monday, May 16, 2005 4:48 PM
- To: ifeffit@millenia.cars.aps.anl.gov
- Subject: [Ifeffit] idealized 95-atom Pt cluster
- Hi,,,
- I'm a new user to Artemis and Atoms. I would like to
generate a simulated
- EXAFS spectrum of an idealized bare 95-atom cluster of
Pt (with no ligands
- attached to it). Looking at Cambridge data files,
the largest cluster
- documented is 18, so I would have to make one up.
I would like to arrange
- the 95 atoms into an idealized sphere with the standard
geometry for bulk
- Pt-Pt bonding that can be predicted from the crystal
structure (e.g.
- metallic radius = 139nm, metallic separation = 277.5nm
separation, etc.)
- I understand this can be done using Artemis and
Atoms. I'm relatively new
- to using the software (prodominantly know how to use
Athena for plotting
- the experimental EXAFS data , not much more).
- Could anyone provide suggestions on how to get started
on this task? E.g.
- Generating the crystal data and displaying the EXAFS of
the resulting bare
- cluster?
- Charles
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