Hi, Several approaches to the problem of a simple, one-shell fit were proposed with different ideas about incorporating them into Artemis: 1. Scott suggested a solution involving a low symmetry group, but ran into a problem that required some knowledge of Feff to solve -- a situation he suggested that Artemis is supposed to protect the user from. 2. Anatoly suggested using Feff's overlap and ss keywords. Those features of Feff were certainly designed for simple fitting problems, but, I agreed with Carlo when he pointed out that the documentation is a bit cryptic. 3. Mark suggested using the Feff templates in Artemis. That's a good idea and certainly why I included the templates, but it fails to protect the user in the manner Scott recommends. 4. Sam explained how SixPack uses simple coordination geometries and a periodic table interface to address this problem. 5. Finally, I suggested one way of solving the problem using Artemis as it is today. Scott made this comment: "So I vote for changing the way Artemis works in such circumstances so that less editing is needed". OK! I agree! We now agree on what we don't want (lots of editing). Now we need to discuss what we *do* want. None of the solutions above are perfect: 1. The low symmetry solution suffers from requiring the user to understand enough crystallography and enough about Feff to get that solution to run to completion. 2. Like Carlo, I have never quite understood the whole overlap thing in Feff. In any case, I think that the user should eventually be forced to think about paths. Today you might analyse the first shell, but tomorrow you will want to roll up your sleeves and start doing a much better analysis. There is no smooth transition from an overlap first shell analysis to a more sophisticated path-based analysis. It is better, IMHO, to start with paths and stick with paths. 3. The problem with the templates is having to know what to write in the templates. The templates are super-helpful if you can, say, cut and paste atomic coordinates from a Protein Data Bank file, but not so convenient otherwise. The solution I see is a combination of Sam's periodic table thing and the solution I suggested two emails ago. It could work something like this: a. Choose "Single scattering fit" from one of the menus b. Pop up a dialog in which the user tells Artemis: i. the species of the absorber ii. the species of the scatterer iii. the approximate distance to the first shell iv. the geometry c. Artemis constructs a suitable feff.inp file, runs Feff without asking for confirmation, and imports only the first path d. Variables for amplitude, sigma^2, delr, and e0 are generated automatically, just like they are now e. Artemis pops up a dialog asking the user if she wants to run the fit immediately or later. The immediate choice is just like the big green button, the later choice lets the user examine things before pressing the big green button. A few comments: Regarding step b.i. and b.ii.: This could be a periodic table, like Sam uses or a couple of entry boxes, which would be more compact Regarding step b.iv.: I think I would include some real diatomic crystal structures, such as rock salt, cesium chloride, zinc sulfide, along with the things in Sam's list (square planar, octahedral, tetrahedral, according to the screenshot on his web site) This approach is simpler than how Artemis currently works only in that it automatically jumps through several steps without stopping. Once the fit is done, the user is still looking at Artemis and Artemis is just as complicated as it ever was. However, the advantage of this approach over, say the overlap thingie, is that one is in a position to begin using some of Artemis' tools to look beyond a simple first shell fit. In short, the bad news is that it is still Artemis, but the good news is that it is still Artemis. Like Scott, we all vote that Artemis work better. But Artemis is the product of a benevolent dictatorship rather than of a democracy. While you all are welcome to cast a vote for the goodness of Artemis, I'm really looking for concrete design suggestions. B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 405 Naval Research Laboratory phone: (1) 202 767 2268 Washington DC 20375, USA fax: (1) 202 767 4642 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/