[Ifeffit] Artemis FEFF for clusters >500 atoms

[scalvin at slc.edu]

Hi Charles,

We didn't use FEFF to create the really large clusters. Instead, we just
generated a FEFF cluster larger than the largest paths we fit, and then
used constraints to deal with all the termination effects. For the
detailed modeling of cuboctahedra (it's been a while--that was the
expected morphology, right?), we reduced the amplitude of each path by the
weighted average of the reduction in coordination number relative to the
bulk for the given morphology and size. A very clever high school student
I was working with (C. J. Riedel) automated the process of generating
these constraints.

This approach is marginally less accurate than letting FEFF figure out an
entire cluster, but doesn't require nearly as much computer power, and
should be pretty darn close for large clusters.

--Scott Calvin
Sarah Lawrence College

> Hi Scott,
> Thanks for your suggestion.  I find that I need to generate FEFF files for
> larger clusters than I had initially started off with. In your recent
> Physica Scripta paper [T115 (2005) 744-748], you had looked at some pretty
> large Pd clusters, particles 0.1 to 200nm in diam. (page 745, col 2, para
> 2, lines 5-6).  Some of these clusters are well over 500 atoms. How did
> you
> manage to create the FEFF?  When I try to do so for a cluster this large
> in
> Artemis, the program flags an error saying that I have too many atoms (in
> my *.inp file generated from TkAtoms).
> Charles
>