switching to FEFF8 in Artemis
I have FEFF8 and would like to get Artemis to use it for EXAFS calculations. I figured out how to use the Edit Preferences menu to point Artemis to the executable and how to get the ATOMS module to use the FEFF8_EXAFS template to generate feff.inp files which result in the generation of feffNNNN.dat files. What doesn't work is that QFS still uses the feff6 template. Without doing something nasty like overwriting the feff6 template with a copy of the feff8 template, how can I get the whole system to work with feff8? Also, I found that when simulating Pu3Ga (a simple Cu3Au structure) out to 10A, feff8 chucked up an error about too many paths, while feff6 did it happily. Is there a way to fix that? How much difference does using feff8 make in terms of proper description of MS paths for k>2, anyway? Do I really win by going through the trouble? mam
Hi Matthew, Your questions never got answered! Yikes!
I have FEFF8 and would like to get Artemis to use it for EXAFS calculations. I figured out how to use the Edit Preferences menu to point Artemis to the executable and how to get the ATOMS module to use the FEFF8_EXAFS template to generate feff.inp files which result in the generation of feffNNNN.dat files. What doesn't work is that QFS still uses the feff6 template. Without doing something nasty like overwriting the feff6 template with a copy of the feff8 template, how can I get the whole system to work with feff8?
Is "QFS" the quick fist shell theory thingie in the Theory menu? You are correct -- it does not give you a choice. Using feff6 is hardwired into it. It seems silly to me to use feff8 for the quick first shell thing, but for the sake of completeness, it should be fixed. Your other option is to run feff8 outside of artemis and import the results. When you "Open file", you can point the file browser at a feff.inp file. That will load the feff.inp file, notice that there are feffNNNN.dat files, and ask how many you want to import. That's the work-around. I would like to understand your problem a bit better so I can improve it.
Also, I found that when simulating Pu3Ga (a simple Cu3Au structure) out to 10A, feff8 chucked up an error about too many paths, while feff6 did it happily. Is there a way to fix that?
One of these might help: http://leonardo.phys.washington.edu/feff/wiki/index.php?title=CRITERIA http://leonardo.phys.washington.edu/feff/wiki/index.php?title=PCRITERIA
How much difference does using feff8 make in terms of proper description of MS paths for k>2, anyway? Do I really win by go ing through the trouble?
Were the question about k>4, I would say with confidence that you do not win. For k>2, I suspect the answer is "not much". For a highly asymmetric material, feff8 should significantly improve the description of the potential surface by virtue of moving charge around self-consistently. But the potentials are still spherical, so there really aren't bonds in feff8. As you move away from the potential surface by increasing energy, you become increasingly insensitive to those details. Is k=2 "far enough" from the potential surface? I don't know. There are a lot of issues down there. k=2 is a region where the details of the background removal are highly correlated with the fit results. Do you need a better feff or a better background removal? It seems like a tough question to answer generally. 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/
Is "QFS" the quick fist shell theory thingie in the Theory menu? You are correct -- it does not give you a choice. Using feff6 is hardwired into it. It seems silly to me to use feff8 for the quick first shell thing, but for the sake of completeness, it should be fixed.
Yes, it's the quick first shell thingie. The problem I have with it defaulting to feff6 is that if the rest of the system is set to use feff8, it will use feff8 as well, but with the *feff6* template, which means that feffNNNN.dat files don't get written. If the QFS system either used feff6, regardless of what version the rest used, or used the same template as the rest, then all would be fine.
Your other option is to run feff8 outside of artemis and import the results. When you "Open file", you can point the file browser at a feff.inp file. That will load the feff.inp file, notice that there are feffNNNN.dat files, and ask how many you want to import.
That's the work-around. I would like to understand your problem a bit better so I can improve it.
It's not a specific problem, but wanting to use the best available calculation. A prominent user on my beamline claims that feff8 is much better for MS, but he hasn't told me what his evidence is.
Also, I found that when simulating Pu3Ga (a simple Cu3Au structure) out to 10A, feff8 chucked up an error about too many paths, while feff6 did it happily. Is there a way to fix that?
One of these might help:
http://leonardo.phys.washington.edu/feff/wiki/index.php?title=CRITERIA
http://leonardo.phys.washington.edu/feff/wiki/index.php?title=PCRITERIA
Sounds like PCRITERIA may be the thing. Of course, that means editing the FEFF file or the template. Is it possible to edit the FEFF file from within Artemis?
How much difference does using feff8 make in terms of proper description of MS paths for k>2, anyway? Do I really win by go ing through the trouble?
Were the question about k>4, I would say with confidence that you do not win. For k>2, I suspect the answer is "not much". For a highly asymmetric material, feff8 should significantly improve the description of the potential surface by virtue of moving charge around self-consistently. But the potentials are still spherical, so there really aren't bonds in feff8. As you move away from the potential surface by increasing energy, you become increasingly insensitive to those details.
So highly-MS-specific things like focusing paths aren't done much better in feff8 than feff6 in the EXAFS range? That's good to know.
Is k=2 "far enough" from the potential surface? I don't know. There are a lot of issues down there. k=2 is a region where the details of the background removal are highly correlated with the fit results. Do you need a better feff or a better background removal? It seems like a tough question to answer generally.
Below k=2., you're solidly in the XANES region, where I know that feff8 doesn't work unless you play with parameters so as to make its output look like the experiment. So far, I have not found a XANES calculator which will give, without adjustment, a realistic-looking XANES curve for even as simple a substance as ZnO, but that's another story. mam
participants (2)
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Bruce Ravel -
Matthew Marcus