There has indeed been progress since FEFF6 -- the newer versions of the program have new input options that the old program will not recognize. E.g., as described in the post Bruce linked to, we now generally use the EDGE card rather than the HOLE card to specify the absorption edge. However the HOLE card is still recognized by the current FEFF9. Someone mentioned FEFF breaking support for older input files. To the contrary I expect FEFF6 input files to work smoothly with the FEFF9 code. E.g. the Cu example in the FEFF6 distribution works with today's FEFF9. FEFF6 and FEFF9 may produce somewhat different output for the same input file because some internal defaults and algorithms have changed.
FEFF9 is not meant to be run through the GUI exclusively. Many users (myself included) love working from the command line, and that will always be 100% supported. The GUI is just another way to control the input file and run the same compiled fortran executables. Occasional users and users unfamiliar with the command-line terminal (the majority of our users work in a Windows environment) seem fairly happy with it. But you can always do the same thing by typing "feff" on the command line.
Our interface still consists of a single text file with 10-20 lines of keywords with options; and then a list of x,y,z coordinates. It's kind of old-fashioned; if something fancier is needed, I'm willing to help or translate it or show interested parties the code.
On to the physics:
I indeed expect that the improved self-energy (we call it MPSE, for Many-Pole Self-Energy) would improve EXAFS for many (not all) materials by shifting peak positions and correcting broadening. Other improvements might come from new options for Debye-Waller factors, TDLDA, or self-consistent SCF potentials (I think some on this mailing may have questioned the value of SCF potentials). The thread referenced by Bruce asks how well one would have to know the dielectric function of a material (that in itself may not be known very precisely) in order to get an advantage from the MPSE. In my own calculations a primitive built-in model requiring no knowledge from the user already seems to provide some of the improvement. It's not a conclusive answer, but it's encouraging. My personal opinion is that the dielectric function does not need to be provided with high accuracy. Josh Kas may be able to make a more qualified statement.
Like Bruce, I would be delighted to see a comprehensive study done. It's certainly on our minds and if anyone else has plans in this direction, I'm sure we would be glad to support the effort.
Finally ... Reading the referenced thread, I feel the need to clarify a few things about the FEFF group... We care a lot about our users and in particular about this community. It's a priority to make our codes useful to this community as well as the wider FEFF community. Personally I spend loads of time responding to questions, testing other people's input files, implementing requests, teaching, ... and wishing I had more time to implement all the remaining things I would like to provide! -- just like Matt or Bruce. I invite everyone to contact me with any FEFF requests that would benefit users, or to include me in ongoing developments. And to end on a cheerful note, I can happily report that FEFF8 for ifeffit EXAFS analysis is ready to be given out!
Cheers and a late happy new year to everyone,
Kevin Jorissen