Hello Marcos: On Wed, 9 Nov 2005, Marcos Eleoterio wrote:
1) After a normalization of the data, i put the data in "Athena" turn on the options: "pre-edge line", "post-edge line" and then "normalized" (in fact i usually turn the option "flatten" on, in dispite of the fact that i don´t know what that means, what that means?), i save using the option "Save chi(k)" in "file".
You can also save an Athena project fie and just that to load data into Artemis.
2)Then i open the program "Artemis" and insert the data saved in the step "1)" in the column of the middle i click with the right button of the mouse and select the option "theory", "atoms" and insert the spatial group, unit cell parameter, and atomic location (here its important to say that the compound that i'm studying is LaCaMnRuO6 the measure of x-ray absorption was performed in the K-edge of the Mn, we are interested in Mn-O ligands so in "Artemis" i only put the data of the Mn and O, right?)
If you are using the known structural parameters for the material, I suggest that you put in all atoms. You can restrict your fitting to the Mn-O first shell if you want but having the entire structure in is helpful. Alternatively, if you are only interested in a quick firt shell fit, there are options for that too in the Theory tab.
3)I click in the option "run atoms" for each atoms that i inserted the information, choosing 10 paths in each step, i click the in the option "run feff" for each atom that i inserted the information (again), after that, i click in "Fit" then appears in the screem the advise: "there is something wrong with your math expressions" (or something like that) i ignore that advise and go on, but the big problem is that the fit appears very poor!
Since you have excluded the non Mn and O atoms, you cannot really fit the data in this simple way. WIth the method you explain, only your first shell paths have any chance of being correct. You will need to restrict your fit to those paths only (the first one or two). Also, you will need to restrict the fitting range to that of the fitrt shell paths. You cannot include the entire range in R-space with this model. In general, even if you include all atoms, it is useful to start only by including the first shell and looking at how the data can be fit in that range. I would not immediately try to fit multiple shells, you need to take it step by step.
I have to say that the information that i use to insert the atomic position, unit cell parameters, was obtained from a Riteveld refinament, that i performed with the data from a cooper x-ray tube, do i need a data from a beam line, at synchroton?
No, not at all, you just need to put all the atoms in. C.S. -- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 Carlo.Segre@iit.edu http://www.iit.edu/~segre