Hi all, There is a new version of GSAS for Windows; Linux to follow soon. The changes are: GSAS News....... April 15, 2004 (tax day in USA) 1. A small cosmetic fix to the g-value editing routine. 2. There is now an option in histogram editing to set aside a certain fraction of the profile points in a powder pattern to calculate an Rfree and Rwfree. This replaces the old 'S' option (which didn't work anyway). The Rfree & Rwfree values appear in the .LST file (not on screen) and in the EXP file. In my initial tests these seem to follow the Rp & Rwp values closely through the entire course of a refinement but maybe you all will see wilder behavior in your refinements. Note that you set two things for this - one is the percentage of points to set aside (1-10%) and a random number seed. The seed ensures that the selection of points remains the same for all runs of POWPREF; this will change if seed is changed or if profile limits & excluded regions are changed. If you want to use this it should be set very early in the analysis; setting it for just the final refinement cycles somewhat defeats its purpose. 3. After some experience, I've had to set the integration controls for the Finger, Cox & Jephcoat axial divergence profile function back to where I had them a few years ago. Too many ripples. New version will be a bit slower but more accurate.
Please let me know of your experiences with Rfree, especially if it differs much from Rp. I'd like to know circumstances when this happens to get an idea of how useful a diagnostic it is. I'm thinking of doing the same for the single crystal histograms - any comments? Enjoy, Bob Von Dreele
