Advanced Photon Source

An Office of Science National User Facility

Powder Diffraction Crystallography Educational Materials

The APS provides on-line materials related to learning to perform crystallographic analysis from powder diffraction.

Introductory Materials
An Introduction to Crystallography
A series of lectures and handout notes given by Dr. Cora Lind 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.

GSAS-II is an open-source Python package appropriate for all types of crystallographic studies, from simple materials through macromolecules, using both powder and single-crystal diffraction and with both x-ray and neutron probes. GSAS-II handles all the steps in diffraction analysis, including data reduction, peak analysis, indexing, Pawley fits, small-angle scattering fits, and structure solution in addition to structure refinement. It can be used with large collections of related datasets for repeated (sequential) refinements and for parametric fitting to these results.

GSAS-II home page
The home page provides information for downloading and installing GSAS-II, citation information, how to report bugs, how to join the mailing list, etc.
Tutorials for learning GSAS-II
The best way to learn to use GSAS-II is to work through some of the 20+ tutorials.

GSAS is an older crystallographic refinement program and EXPGUI is a graphical user interface for GSAS. These two programs are no longer being developed or supported. Users are encouraged to use GSAS-II instead. The educational material here is of value for learning the basics of Rietveld refinement.

EXPGUI home page
Information on downloading and installing GSAS and EXPGUI can be found here.
An Overview of GSAS and EXPGUI
An 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 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 Rietveld 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 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. Topics include: Installing the software, How to get starting profile terms, Getting coordinates into GSAS, Graphics options in EXPGUI, Simulation of diffraction patterns, Bootstrapping the background, Returning to a prior refinement, Changing flags & settings for multiple histograms en mass, Creating and Viewing Fourier Maps, Constraining Atom Parameters, 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.

CMPR is a multipurpose program that can be used for displaying diffraction data, manual- & auto-indexing, peak fitting and other nifty stuff.  CMPR is no longer being developed or supported.

CMPR home page
Provides download, mail list links, etc. as well as a link to documentation and installation instructions for all common types of computers.
Installing CMPR in Windows
This shows how CMPR is installed onto a windows XP computer using a self-upgrading installer. (12 min)
Upgrading CMPR with the self-updater
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. (2 min)
Switching between CMPR versions
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. (5 min)
Reading a data set and fitting diffraction peaks
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. (31 min)
Running the Autoindexing Programs
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. (25 min)
Mini-symposium: A Century of Powder Diffraction

Powder diffraction was developed independently in 1916 by Peter Debye and Paul Scherrer in Germany and Alber Hull in the U.S. To commemorate the 100th anniversary, a half-day symposium on historical developments in powder diffraction as well as contemporary APS work was held on November 11, 2016. Speakers included: David Cox (Brookhaven National Laboratory, Retired), Tim Fawcett (International Centre for Diffraction Data) Pete Chupas, Andrey Yakovenko, Saul Lapidus, Olaf J. Borkiewicz, Robert B. Von Dreele (affiliation is Advanced Photon Source, Argonne unless otherwise noted). Talks are available on-line: see program.