Charles,
When you asked me this in private email last week, I did not completely understand the question.
One (simple) solution to your question is to run Atoms on crystalline Pt and have it write out a cluster of the approximate size. For instance, a 7 angstrom cluster contains 87 atoms. I am guessing that the exafs from that will be pretty similar to the cluster you are looking for.
Of course, there are truncation effects. The cluster you are interested in will have some geometry which may not be well approximated by a sphere. Also, one must worry about the attenuation of coordination numbers due to absorption by atoms at the perifery of the cluster.
Also, remember that Atoms is a crystallography code. If you are interested in a cluster of atoms that is not a crystal, then you will need some other mechanism for generating the list of atomic coordinates needed by Feff.
Many people, including some some of the frequent contributors to this mailing list, have done considerable work on exafs of metallic nanoparticles. You should look up papers by Anatoly Frenkel and by Scott Calvin (and probably others as well) to see how some of the exafs experts who have already done work in this field have addressed your problem.
HTH, B
I tried this out, but some difficulties when attempting to plot with Artemis. I generated the Pt cluster with TkAtoms ver. 3.0beta9 running perl S.006001 and Tk800.024 and produced the "feff.inp" file. (My computer operates under Windows XP.) I tried to plot with Artemis 0.7.015(c) after importing the *.inp. file. (To my understanding, these are the most up-to-date program versions.) I get a message, "Artemis trapped one or more errors! Error message dumped onto screen." I'd like to see what the errors are in order to figure out how to fix for proper plotting, but when I go to the "view message" window (under "Edit" menu), it is blank. Not obvious where the error message(s) are displayed. Is there another location in the Artemis program that the error message should be if not in this window? Charles