[Ifeffit] XANES

[John J. Rehr]

Hi Matt,

 It's not clear to me that FEFF has to be changed at all to get a tensor
XANES calculation going. The code simply has to be rerun a few times with
different input. Anyway, The FEFF8.2 license now allows users to make changes
that improve input/output. 

 Also various modules of FEFF are now redistributable in order to
facilitate user developments in response to previous suggestions
from Matt and Bruce. This seems to be a good way to go, since much
of FEFF is an engine that shouldn't be messed with. Also much of
FEFF6 is now distributed with IFEFFIT. These EXAFS parts of the code are
very stable/reliable. It doesn't seem desirable to me to freely distribute
more recent parts that are less well developed. On the other hand we will
and do work with various collaborators on various code developments.

 I'd like to hear from other users/developers of their concerns
about the FEFF license. Funds from the license fee do go to
the UWOTT to support the FEFF project (equipment supplies, travel
etc.). 

 John

> On Tue, 4 Mar 2003, John J. Rehr wrote:
> 
> >  Doing XANES fits ala Benfatto and Della Longa would also be
> > desirable in the long run, i.e., fitting the XAS(x) with x
> > standing for various parameters like interatomic distances. To
> > do that would generally require looping over the FMS module in
> > FEFF and could get time consuming. To avoid this, one needs
> > something like a tensor XANES calculation, which computes d mu/
> > dx via multiple XAS calculations and hence permits fast linear
> > interpolations. This is not implementable with IFEFFIT/ATHENA
> > at present as far as I know. However, I don't see major
> > difficulties in implementation (?).
> 
> Well, it wouldn't be easy, but it is technically feasible. Bruce
> and I have been pushing for changes to Feff that would facilitate
> these and other important capabilities for many years now.
> 
> The main difficulty is a legal one.  The Feff license forbids
> anyone from altering Feff8 and distributing the changes.  So I
> agree when you say that these changes cannot be implemented
> within IFEFFIT.  This is not for any technical reason, but simply
> because you do not allow it to happen.  You are unwilling to
> change the code to allow these things, and forbd anyone else from
> making such changes.
> 
> This is not an unfortunate but unavoidable consequence of an
> otherwise beneficial license.  No, it is the entire point of the
> Feff license to restrict others from developing new capabilities
> exactly of this sort.  There is no other explanation for the
> license.  The scientific merit of this policy is beyond my
> comprehension, but the restriction is completely deliberate.
> 
> Perhaps the more surprising thing is that Feff has never included
> analytic capabilities, but is widely used for EXAFS analysis.  
> In this respect, Feff is very unusual for scientific software.  
> Since those working on analysis codes are forbidden from changing
> Feff, it's not very likely that significant progress will be made
> in XANES analysis or other new areas unless you pay attention to
> the requests and suggestions of experimentalists and authors of
> analysis codes.  History is does not on your side.
> 
> And yet from the above statement, you see these capabilities for
> XANES analysis as technically possible and desirable.  I agree
> with this, but don't see how they can possibly be done given the
> very clear intention of the Feff license.  I cannot imagine
> anyone willing and able to make these changes.
> 
> Since you think these capabilities for XANES analysis are both
> desirable and possible, it would be interesting to hear why you
> think it is in the best interest of the XAFS community for the
> Feff Project to prevent the development of such capabilities.
> 
> --Matt
> 
> 
> 
> 
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