Hello, I am looking for some help on trying to understand what is wrong with our data. We are very impressed with the high values of amplitude (up to 390.24) that we got working with Artemis and we know are wrong. Hope somebody could help us and take a look into these files, we will appreciate it. Thank you in advance!
Hello,
I am looking for some help on trying to understand what is wrong with our data. We are very impressed with the high values of amplitude (up to 390.24) that we got working with Artemis and we know are wrong. Hope somebody could help us and take a look into these files, we will appreciate it.
Thank you in advance!
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit I am not familiar with Feff8 INP files but it seems there are too many O
On 8/11/2010 5:41 AM, Edgar Macias wrote: paths in the Feff calculations. It calculated scattering paths using the Cu-O 2nd nearest neighbor as Ru-O 2nd paths which doesn't exist. You can see this if you have crystallographic software that allows measuring atomic distance between atoms such as Balls&Sticks which is free software and quite useful. All of the other distances correlate to the distances from the structure. buena salud, -- Chris Patridge PhD. Candidate Dept. of Chemistry SUNY University at Buffalo Buffalo, NY 14260 Contact: 315-529-0501
On Wednesday 11 August 2010 05:41:41 am Edgar Macias wrote:
I am looking for some help on trying to understand what is wrong with our data. We are very impressed with the high values of amplitude (up to 390.24) that we got working with Artemis and we know are wrong. Hope somebody could help us and take a look into these files, we will appreciate it.
Hi Edgar, There is much to be concerned about in your fitting model, but the concern that prompted yor post to the list is not one of them. It would seem that the version of Feff that you are using did not rescale its importance factor correctly when it ran into the situation that the second path has a higher importance than the first. The importance factor is not used for any real purpose either in Feff or in Ifeffit. Artemis displays as an aid to understanding the paths, but does not use it in any manner in the fit. So I think you are worried about something that isn't a problem. So ... what should you be worried about? Certainly a couple of things: 1. I don't understand the purpose of importing the exact same data twice and then assigning different Feff calculations to each copy. Is you intent to model a mixed phase system? That seems likely given that you defined an "x" parameter then did things like "x*amp" and "(1-x)*amp" in the paths. If you are trying to model a mixed phase system, you need to import your data *once* and assign multiple Feff calculations to it. The data and path list should look something like this (my little sketch will probably make sense only by using fixed-width font): - Data - Feff #1 Path 1 Path 2 - Feff #2 Path 1 Path 2 2. Perhaps you did have a reason to import the data twice. If so, it is not clear why you set the k-range to a sensible [2:13.3] in the second copy, but to [1:6] in the first copy. 3. I'd be sceptical that you could meaningfully measure independent E0 parameters for the two phases. Maybe, but you should look at that with a critical eye. If you have not spent some time with the information about using Artemis that can be found at http://xafs.org , then you probably should do so. HTH, B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
participants (3)
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Bruce Ravel -
Chris Patridge -
Edgar Macias