GSAS-II Home

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 in the future, neutron TOF.) At present, code is being developed for all the various steps in diffraction analysis, such as data reduction, peak analysis, indexing, structure solution and structure refinement. The source code can be found at ​https://subversion.xray.aps.anl.gov/pyGSAS/trunk/

At present GSAS-II can be used for processing of area detector data, peak fitting, auto-indexing, structure solution, Pawley and Rietveld fitting. Many of the nice features of GSAS are present and some things work much better than in GSAS, but other features are yet to come. At this point only x-rays and constant wavelength neutrons are implemented (no TOF). The GUI is self-documenting with help pages for every GUI page. The code is changing on a regular basis, so expect things to break from time to time and you should 'Update' frequently to stay abrest of new features as they are added.

If you use GSAS-II, please sign up for the GSAS-II mailing list, see web page ​http://www.aps.anl.gov/mailman/listinfo/GSAS-II.

Installation instructions

• Windows
• Mac OS X
• Linux

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 User Documentation

Help file: ​https://subversion.xray.aps.anl.gov/pyGSAS/trunk/help/gsasII.html

Tutorials (help file may include newer tutorials not listed here)

• ​Starting GSAS-II
• ​Powder pattern peak picking, fitting and indexing
• ​Lab X-ray powder pattern Rietveld refinement
• ​CW Neutron powder pattern Rietveld refinement with constraints
• ​Combined neutron x-ray Rietveld refinement and Fourier maps
• ​2-D Image calibration
• ​2-D Image integration

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 at mailman.aps.anl.gov" GSAS-II-request@…. Use subject subscribe (or subscribe <password> where <password> is your preference for a mailing list login password).

• ​to see archives (​https://mailman.aps.anl.gov/pipermail/gsas-ii/)

• Starting Oct 2013, e-mail is also archived at ​http://www.mail-archive.com/gsas-ii@mailman.aps.anl.gov/.
  Search that archive here:

GSAS-II Project tracking

Updates to the source code can be followed using the ​Timeline Trac tool at this website. To enter a ticket, send an e-mail to Brian Toby. The Roadmap feature is not currently in use.

GSAS-II Developer Notes

A section of this Wiki is reserved for Code Developers. This includes an extensive guide to the code.

For a complete list of GSAS-II wiki pages, see TitleIndex.