Re: [Ifeffit] FEFF report: Hard tests failed in fovrg.

Dear Ifeffit community, a short reaction from the FEFFgroup. 1/ It's true that we don't follow up on the ifeffit ML 100%. Important issues usually do get through to us. We highly value the ifeffit community. We can also be contacted directly for problems that are FEFF related rather than iFEFFit related ( contacthttp://www.feffproject.org/feffproject-contact.html ). We'll likely ask you for the feff.inp file that generates the problem. 2/ We're glad that FEFF6 is so successful. Meanwhile FEFF6 is about as old as Windows95, and development is now focused on FEFF9http://www.feffproject.org/feffproject-feff.html, which has 15-20 years of improvements over FEFF6. It's a big improvement for anyone running FEFF calculations. It costs $500, or $250 upgrade from any paid version of FEFF. 3/ The OP posted 5 input files. 4 of these run without problems in FEFF9. The last has I atoms (Z=53) at a spacing of 0.8A, and doesn't run out of the box. I expect the same result from FEFF8. 4/ There has been some effort to bring a "FEFF9lite" to the analysis codes, analogous to the FEFF6lite discussed here. We would be very happy to see that effort succeed. 5/ FWIW the fovrg routine was retired in 1996 and replaced by a relativistic version called "dfovrg". The "hard error" does not exist anymore. 6/ We're a small team; we apologize for all the 'bothering' we don't get around to. We do care about supporting our users and put a lot of energy into support. Please reach out ot us when you need us. Cheers from Seattle, Kevin Jorissen PS I posted a while back about a problem with JFEFF and Java updates but I'm not sure the message made it through: I asked the mod, but no reply. I hope this msg makes it :). On Wed, Aug 7, 2013 at 8:24 AM, Bruce Ravel wrote:

On 08/06/2013 11:55 AM, Naumova, Maria wrote:

...

May I use this FEFF calculation as a valid base for future fit? Or this error means that FEFF doesn't work correct and I can't rely on its output? If the phase-shift program failed to converge does it mean that it could stop in some completely unrealistic result?

Maria,

You are correct that the version of Feff6 that we are allowed to give away for free reliably complains about failing something called a "hard test". This is some kind of convergence test on the computation of the muffin tin potential.

The test is made in the lines just prior to this:

https://github.com/newville/**ifeffit/blob/master/src/feff6/**fovrg.f#L158https://github.com/newville/ifeffit/blob/master/src/feff6/fovrg.f#L158

The error is reported here:

https://github.com/newville/**ifeffit/blob/master/src/feff6/**phase.f#L127https://github.com/newville/ifeffit/blob/master/src/feff6/phase.f#L127

If you can make heads to tails out of the calculation in fovrg.f, you are vastly smarter than me, vastly more patient than me, or both!

I have 2 comments on the main point of your post:

1. As you noted, this question has been asked many times before. Not once has anyone from the Feff project (i.e. anyone who might actually have a working knowledge of that bit of code) bothered to comment. It would be lovely to hear from one of them.

2. This very version of Feff has been included with Ifeffit and with the packages I build for my software for years. Over a decade, in fact. In that time, Feff, Ifeffit, and my software have been used for defensible data analysis thousands of times and by hundreds of practitioners.

That does not mean that any part of the software stack is actually correct. But it does mean that lots of article writers and lots of article reviewers have accepted the results coming from this stack of software.

That does not mean that you should accept it. Quite the contrary -- you would be wise to question every part of the software stack. You may even find that you will need to discard any or all parts of that software stack and replace them with something you trust more -- perhaps even with something that you, yourself have written.

To summarize, I am saying the same thing I have said in the past. I don't understand the code that generates that message. No one from the Feff project has ever bothered weighing in on what it means. No one has demonstrated that it represents an actionable problem. The codes which use Feff have been in use for years to produce defensible science.

So, in conclusion, what should you do? I have no idea. My advice is to continue using the software, but my advice may not be any more reliable than the software itself.

I hope that helps. Probably doesn't, but it's the best I can do. B

-- Bruce Ravel ------------------------------**------ bravel@bnl.gov

National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973

Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel ______________________________**_________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.**gov http://millenia.cars.aps.anl.**gov/mailman/listinfo/ifeffithttp://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit