The Advanced Photon Source
a U.S. Department of Energy Office of Science User Facility

Powder Diffraction Crystallography Resources

This page (from 2006) references a series of demos and lectures that introduce Rietveld analysis techniques. Note that  use of GSAS-II is now recommended over GSAS/EXPGUI.

Introductory Talks

An Introduction to Crystallography (University of Toledo Chem 4980/6850/8850)

A series of lectures and handout notes given by Dr. Cora Lind-Kovacs for her Chem 4980/6850/8850: X-ray Crystallography course at the University of Toledo (Ohio). These lectures introduce concepts in crystallography, such as the lattice, symmetry, single-crystal and powder diffraction, crystal structure determination and refinement.

Getting Started with Rietveld

A Flash movie presentation reviewing background concepts needed for Rietveld analysis and introducing how the Rietveld method works.

Space Groups: A primer on topics significant for powder diffraction

A Flash movie presentation discussing space group naming, subgroup transforms and their importance in phase transformations, and how space groups are input to GSAS, as well as common errors made in settings.

A Casual Introduction to Least-squares Fitting: A [mostly] descriptive approach

A non-rigorous introduction to linear algebra, linear and non-linear least squares and related concepts.

Software Tutorials

An Overview of GSAS and EXPGUI

A Flash movie introduction to the GSAS software for Rietveld analysis and the EXPGUI interface to GSAS, presenting some history and an overview of functionality, concentration on the organization and features of the graphical user interface.

GSAS/EXPGUI demo: CW Neutron Alumina Example

A Flash movie/web demo that steps through a simple, but complete fit to a set of constant wavelength neutron diffraction data using EXPGUI as an interface to GSAS.

GSAS Parameters & Controls What to Refine when? (Refinement Recipes)

A 90 minute Flash movie talk that presents GSAS controls and refinable parameters. Particular emphasis is made on profile terms.

Le Bail Intensity Extraction

The Le Bail method optimize a fit to powder diffraction data treating reflection intensities as arbitrary. This presentation is a Flash movie lecture that introduces the Le Bail method, explains why it can be valuable and discusses tools and strategies for Le Bail fits with GSAS.

Judging quality: Catching common refinement problems

A Flash movie presentation that presents how to judge quality of Rietvelds fits.

Combined Rietveld Refinements: Where 1+1 can be > 2

A Flash movie presentation that discusses how to use additional experimental measurements or a priori knowledge to fit more complex models. Also presented are some of the potential problems that can occur.

Advanced Topics

Advanced Rietveld Techniques: Tricks and Tips with EXPGUI

A web/video version of a presentation presenting advanced topics on use of GSAS & EXPGUI and related software, such as CMPR and DRAWxtl. The presentation consists of 20 flash movies showing:

  1. Installing the software
  2. How to get starting profile terms
  3. Getting coordinates into GSAS
  4. Graphics options in EXPGUI
  5. Simulation of diffraction patterns
  6. Bootstrapping the background
  7. Returning to a prior refinement
  8. Changing flags & settings for multiple histograms en mass
  9. Creating and Viewing Fourier Maps
  10. Constraining Atom Parameters
  11. Other Tips, Tools & Tricks

ACNS Magnetic Structure Analysis Workshop

A set of web pages with reference materials from the workshop titled "Magnetic Structure Analysis from Neutron Powder Diffraction Data Using GSAS" presented at the 2006 American Conference on Neutron Scattering held in St. Charles, IL, June 18-22, 2006. This includes lecture notes from all presenters, a set of exercises, and a Flash movie made of the demo for the first exercise.

Learning to Use CMPR

CMPR is a multipurpose program that can be used for displaying diffraction data, manual- & auto-indexing, peak fitting and other nifty stuff. The home page for CMPR provides download, mail list links, etc. as well as a link to documentation and installation instructions for all common types of computers. Below are links to recorded demos that show installation and use of the program:

Installing CMPR in Windows (12 min)

This shows how CMPR is installed onto a windows XP computer using a self-upgrading installer.

Upgrading CMPR with the self-updater (2 min)

The preferred way to install CMPR uses the SVN (subversion) program to install the software automatically from a web server. The software can be loaded in as a static install where web connectivity is not required, but when the software is loaded in this self-updating fashion, it the latest updates can be obtained at any time through a menu command, as shown in this demo.

Switching between CMPR versions (5 min)

When CMPR is installed as self-updating, two versions of the program are installed. One, the standard or stable version has only changes that have been tested. The development version has the latest ideas for the program implemented. The changes may fix bug or introduce new ones, as new capabilities are added to the program. This demo shows how easy it is to switch back and forth between the versions.

Reading a data set and fitting diffraction peaks (31 min)

In this example, a data set is read in from file, and then small sections of the pattern are fit a few peaks at a time. Finally, the original data and the results are saved as a CMPR project.

Running Autoindexing Programs (25 min)

CMPR provides an interface to the ITO, DICVOL06 and N-TREOR autoindexing programs. In this example, possible unit cells to index the peaks from the previous demo are identified.