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
large Pd clusters, particles 0.1 to 200nm in diam. (page 745, col 2,
Re: [Ifeffit] Artemis FEFF for clusters >500 atomsIn the articles by Montejano-Carrizale et al, Nanosctructured Materials, v.1, 397 (1992) and v.8, 269 (1997), analytical expressions are published for the 1NN coordination numbers in different geometries, including cuboctahedral, as a function of the cluster order L. However, to fit the entire r-range, one has to know how the 2NN, 3NN and multiple-scattering paths depend on the cluster order. Very similar to what Scott described, we also calculated these truncation parameters for SS and MS paths, for any given cluster order L, but they were not parameterized during the fit since it requires to know analytical expression N(L) where N is the truncation parameter and L is the cluster order. Instead, we just wrote several programs - coordination number generators - for different geometries: cuboctahedral, icosahedral, octahedral, truncated octahedral, and for each geometry and for each size we obtained the truncation parameters for parsing the x,y,z coordinates through another program that we wrote, that calculates the radial distribution function relative to the central atom. By EXAFS data analysis we obtained the coordination numbers for SS and MS paths model-independently and then compared them against several models of different sizes (L) and morphologies. Here are some references: J. Am. Chem. Soc., 119 , 7760 (1997) , J. Synchrotron Rad., 6 , 293 (1999). J. Phys. Chem. B, 105, 12689-12703 (2001). Anatoly -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov]On Behalf Of scalvin@slc.edu Sent: Monday, May 30, 2005 9:08 AM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Artemis FEFF for clusters >500 atoms 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 pretty 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
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