Version 58 (modified by toby, 5 years ago) (diff)



GSAS-II is an open source Python project that addresses 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. Measurements can be constant wavelength or TOF (thanks to support from Oak Ridge National Lab.) It provides structure solution and refinement as well as extensive visualization capabilities. For powder diffraction, GSAS-II offers preliminary stages of analysis, including area detector integration, pattern indexing, LeBail and Pawley intensity extraction and peak fitting. Small-angle scattering and reflectometry fitting is also supported. When large numbers of patterns are measured with parametric changes in measurement settings, a single combined refinement offers parametric fitting. GSAS-II is made available for free use (see license) with open access to the source code.

We are adding new features to the code quite frequently, so we may break things from time to time (see bug reporting, below). Be sure to 'Update' frequently to stay abreast of new features and fixes as they are added.

GSAS-II now provides all of the capabilities in GSAS/EXPGUI, which are no longer supported. GSAS/EXPGUI users are encouraged to switch to use of GSAS-II.

If you use GSAS-II, we encourage you to sign up for the GSAS-II mailing list (see below). Please help us by citing it in your papers.

Installation instructions

The license for use is included with the software and is found here. Also, please sign up for the mailing list after installing GSAS-II.

GSAS-II and Python 3.x: We are now supporting GSAS-II with Python 3.6 & 3.7 and wxPython 4.0. It works and have tracked down most of the bugs with these versions, but this still needs more testing before we make Python 3 the default. We do ask users to try this out. See Python3 notes for more details.

Please Cite

The primary citation for GSAS-II is:

Toby, B. H., & Von Dreele, R. B. (2013). "GSAS-II: the genesis of a modern open-source all purpose crystallography software package". Journal of Applied Crystallography, 46(2), 544-549.

If you use GSAS-II in any part of your project, please cite it in your publications. This is the only way you can demonstrate your support of the project. (Citations to GSAS-II have ~doubled every year, with 104 citations in 2017.) Note that some sections of program utilize work by others and will display citations for that. If you use those sections, please cite those papers as well.


To learn how to use different parts of GSAS-II, we strongly encourage running the tutorials here. Note new addition of many video-tutorials so you can see the computer screen as the tutorial is being run.

For background material on powder diffraction crystallography, see the links on our Powder Diffraction Crystallography Educational Materials page.

GSAS-II Documentation

In the future we hope to increase the amount of documentation available but for now this is what is available:

  • Developer Notes: ~200 pages of code documentation are on a separate web site. This is probably not valuable to most users, but code developers should look here. We invite people interested in developing or extending GSAS-II. The code is open source and we are happy to consider collaborations.

Mailing List

Please do subscribe to the mailing list, or use the archives to look for announcements:

  • To subscribe use this link for the Web interface or send an e-mail to "GSAS-II-request @" (remove spaces). Use as the subject subscribe (or subscribe <password> where <password> is your preference for a mailing list login password).


We frequently get bug reports without enough information to find what is wrong or that might have already been fixed. Before reporting a bug, please confirm you are using the newest GSAS-II version (see !Help/"Check for Updates"). If in the latest version, and we can reproduce your bug, we will work on fixing it. Suggestions for improvements are also welcome.

To report a bug, either send an e-mail to the mailing list (gsas-ii "at" or send it to both of us (vondreele "at" and toby "at" Also, please do the following:

1) Send us the error message(s) and traceback from the console window [text beginning with "Traceback (most recent call..."]. Also, tell us if you are running on Windows, Mac or Linux (it sometimes matters).

2) Get us the .gpx file — don’t send that to gsas-ii@…, but you can e-mail it to toby@… and vondreele@…. Better still, upload it to (you will need to set up a guest account) or use some other sharing service, such as; include a link in the e-mail.

3) Please say what you need to do to reproduce the error from the .gpx file (please provide a detailed list of menu commands, button clicks, etc. so we can duplicate that.) If we can't reproduce it, we can't fix it.

4) If your error involves processing an image, we will need that too. Again please don’t send that to gsas-ii@…, either.

GSAS-II Project tracking

Lists of the updates made to the source code can be followed using the Timeline Trac tool at this website. Tickets and the Roadmap feature are not currently in use.

APS User's Group

Topical meetings, intended for Argonne-based scientists, are held usually on the second Monday of each month, 1-2 pm in 401/B4100. See the Users Meeting web page page for information on past and future meetings.

A complete list of GSAS-II wiki pages is here.'