• Introduce advanced & less obvious features of EXPGUI
• Format: Problems & Solutions

• Crystallography
• Some experience with GSAS & EXPGUI
• Desire to learn new tricks & easier approaches

0. Installing the software

   This section shows how GSAS, EXPGUI, CMPR & DRAWxtl (and GRACE) are obtained and the demo shows the installation of the software on a PC running Windows.

               Presentation Notes
               Demo: Installing & updating GSAS & EXPGUI (10 min)
               Demo: Installing CMPR & DRAWxtl (8 min)
               Demo: Customize EXPGUI to start in a selected directory (1 min)
    
1. How to get starting profile terms

   Problem: Starting a refinement with bad profile coefficients & only an approximate structure is quite hard
   Solution: In CMPR, fit peaks widths and then fit a profile function to the widths; then in EXPGUI write the profile function into an instrument parameter file

               Presentation Notes
               Demo: Fit widths and fit a profile function (15 min)
               Demo: Use INSTEDIT in EXPGUI to write profile values into an instrument parameter file (9 min)

2. Getting coordinates into GSAS

   Problem: How do I get coordinates electronically into GSAS without retyping them?
   Solution: EXPGUI can read a variety of coordinate formats, most importantly CIF; it can reset Origin 1 settings into Origin 2; atoms can also be displayed in an order other than the sequence they have been input.

               Presentation Notes
               Demo: Import Coordinates into EXPGUI from a CIF (7 min)
               Demo: Transfer Origin 1 settings to Origin 2 (4 min)
               Demo: Change display order of atoms (1 min)
3. Graphics options in EXPGUI

   Problem: Are there good ways to graphically review my fit or structure? Can
   Solution: EXPGUI includes LIVEPLOT for review

               Presentation Notes
               Demo: Reviewing fits with LIVEPLOT; survey of LIVEPLOT capabilities (7 min)
               Demo: Exporting graphics and data from LIVEPLOT (3 min)
               Demo: Exporting diffraction data from GSAS into CMPR (3 min)
               Demo: EXPGUI interface to DRAWxtl to display molecular graphics (6 min)

4. Simulation of diffraction patterns

   Problem: How can I easily simulate a diffraction pattern, for example from a CIF?
   Solution: Use EXPGUI to set up the simulation for GSAS.

               Presentation Notes
               Demo: Using EXPGUI to do quick diffraction simulations with GSAS (6 min)
    
5. Bootstrapping the background

   Problem: Fitting background is easy, except when the structure, profile and initial background are all wrong (or when doing a Le Bail fit). How can I just put the background where I want it to be?
   Solution: Use of fixed background points is not a great idea, but using such points to generate an initial background model that is later refined when the model is in good shape. BKGEDIT can be used to do exactly that.

               Presentation Notes
               Demo: Using BKGFIT to fit tough background problems (16 min)

6. Returning to a prior refinement

   Problem:Yesterday's Fit Was Better Than What I Have Done Since. How Do I Get It Back?
   Solution:GSAS keeps a historical list of old experiment files. EXPGUI has a tool to browse them and load one.

               Presentation Notes
               Demo: Reviewing and loading a previous refinement with the "include archived files" feature (5 min)
    
7. Changing flags & settings for multiple histograms en mass

   Problem: I have a 10 histogram refinement with 3 phases, but I don't want to have to edit 10 sets of background parameters or 30 sets of profile refinement flags. Can I set everything at the same time?
   Solution: Yes - use multiple histogram selection.

               Presentation Notes
               Demo: EXPGUI features for simplifying multiple dataset refinements (10 min)

8. Creating and Viewing Fourier Maps

   Problem: How do I create and analyze Fourier maps.
   Solution: Fourier maps are set up in EXPEDT (not EXPGUI, sorry); GSAS has tools for finding peaks in the map, as well as plotting them; Another option is DRAWxtl, which plots structures and maps quite nicely.

               Presentation Notes
               Demo: Setting up and computing a difference Fourier map (7 min)
               Demo: Exporting a Fourier map and viewing it in DRAWxtl (8 min)
    
9. Constraining Atom Parameters

   Problem: When I refine all the atomic parameters in my model, the structure blows up. How do I deal with two atoms that share a site, etc.?
   Solution: GSAS allows the number of refined parameters to be reduced by forcing the shifts on more than one parameter to be the same (or related by a ratio). EXPGUI offers some tools to make this easier to do, particularly when two atoms are placed at the same site and the fraction of the two atoms is to be varied while the total occupancy is to remain constant.

               Presentation Notes
               Demo: Setting up GSAS atom contraints in EXPGUI (9 min)

10. Other Tips, Tools & Tricks

    Problem: How do I learn about other obscure features in EXPGUI, without reading the tedious and humorless web-page documentation that comes with the software?
    Solution: You can learn some cute tricks here: controlling output in the .LST file; tricks in LSTVIEW, using detachable menus, benefits of the "Change Profile" window; the composition tool; editing excluded regions. Don't look for much humor here either.

                Presentation Notes
                Demo: Miscellaneous EXPGUI tricks (17 min)

APS Powder diffraction crystallography instructional materials overview