Hi Scott, Thanks a lot for the insight. It seems like it'll take a bit of work, but I'm happy to hear it's doable.
best, Carl On Thu, May 29, 2014 at 12:54 PM, Scott Calvin <scal...@sarahlawrence.edu>wrote: > Dear Carl, > > The short answer is yes, but it takes a little bit of effort. > > One method is to actually figure out how stretching the c-axis impacts the > lengths of each path geometrically, and then use the functions determine to > express the delr's of each path in terms of the change in c. This method is > rigorously correct, but requires digging in to the geometry, and entering > somewhat lengthy expressions for many of the scattering paths. > > A related method is to in effect use a first-order approximation of those > changes. To do that, create two atoms files with slightly different values > of c. Generate the corresponding paths, and see how the reff of those paths > changes. For example, changing c by 0.01 might result in a certain path > having a reff change by 0.014. Use the ratio of the change in reff to the > change in c to scale the delr of those paths with respect to a guessed > parameter delc. In the example I just provided the delr of the path in > question would be chosen to be 1.4*delc. > > The second method is, of course, approximate, but for small changes in a > parameter such as c can work pretty well, and can be easier to implement > than the first. > > --Scott Calvin > Sarah Lawrence College > > > On May 29, 2014, at 12:33 PM, Carl Brozek <bro...@mit.edu> wrote: > > > Dear All, > > > > Thank you for your responses so far and I apologize for not being > clearer. > > > > Here is the problem at hand: I have a material that is best thought of > as organic, graphene-like 2-D sheets connected by infinite chains of Fe-S. > Based on PXRD and other techniques, we know the structure of the AB plane > (the 2-D organic part), but we aren't able to make sense of what is going > on with the Fe-S chain. We can simulate the PXRD based on proposed .cif > files, but it's off most likely because of the c direction (Fe-S chain). > > > > We collected Fe K edge XAS to tease out Fe-S bond angles and distances, > hoping we could feed this into our simulation for the PXRD to improve the > fit. > > > > Modifying the ATOMS input by hand, by constructing different reasonable > geometries, was improving the simulation, but using a error minimization > fitting program would be best. > > > > So, is it possible to vary specific angles and distances between atoms > along the c-direction only in an error minimization program based on our > experimental data? > > > > I apologize if you have already responded to this reformulated question. > > > > best, > > Carl > > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > -- PhD Candidate | Chemistry | MIT SB | 2010 | University of Chicago
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