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Information about GSAS

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GSAS (General Structure Analysis System) is a comprehensive system for the refinement of structural models to both x-ray and neutron diffraction data. The GSAS package can be used with both single-crystal and powder diffraction data (Rietveld analysis), even both simultaneously. Neutron data can be either from single-wavelength instruments, or for those a bit more masochistic, time-of-flight instrumentation. Up to 99 different sets of data can be modeled using mixtures of up to 9 different phases.

GSAS has been created by Allen C. Larson and Robert B. Von Dreele of Los Alamos National Laboratory. Executable versions of GSAS are distributed more-or-less freely (see the friendly message from the Regents of the University of California, below), but the source code is not distributed.

EXPGUI is a graphical user interface that makes GSAS easier to learn and use, at least for most new users. GSAS and EXPGUI are distributed together from this site.

Installation instructions: Windows, Mac OS X, or Linux
GSAS Manual:
Web educational materials:
EXPGUI documentation:

GSAS manual

The GSAS manual is included with the distributions of the GSAS programs (see above) or can be downloaded here. It is a ~230 page PDF file (1.7Mb) that contains three sections: tutorials, mathematical basis & file structures. Every GSAS user should take the time to read the "mathematical basis" section! (See pages 125-179 in 1/19/01 version) The manual is what you should cite when publishing a structure refined with GSAS (see below).


The folks that have written GSAS get very little credit for their massive efforts. By including a reference to GSAS in your papers, you can help see that the citation index will reflect the importance of their contribution.

  • A.C. Larson and R.B. Von Dreele, "General Structure Analysis System (GSAS)", Los Alamos National Laboratory Report LAUR 86-748 (2000). link to GSAS Manual

Much of the same is true for EXPGUI.

GSAS is written by: Allen C. Larson and Robert B. Von Dreele MS-H805, Los Alamos National Laboratory, Los Alamos, NM 87545. Problems, questions or kudos concerning GSAS should be sent to Robert B. Von Dreele at vondreele@…

GSAS is Copyright, 1984-, The Regents of the University of California. The GSAS software was produced under a U.S. Government contract (W-7405-ENG-36) by the Los Alamos National Laboratory, which is operated by the University of California for the U.S. Department of Energy. The U.S. Government is licensed to use, reproduce, and distribute this software. Permission is granted to the public to copy and use this software without charge, provided that this notice and any statement of authorship are reproduced on all copies. Neither the Government nor the University makes any warranty, express or implied, or assumes any liability or responsibility for the use of this software.

Neither any author nor the U.S. Government makes any warranty, expressed or implied, or assumes any liability or responsibility for the use of this information or the software described here.