[Ifeffit] idealized 95-atom Pt cluster

[Charles Chusuei]

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 at millenia.cars.aps.anl.gov 
>[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov]On Behalf Of Charles Chusuei
>Sent: Monday, May 16, 2005 4:48 PM
>To: ifeffit at 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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