NCNR'S user-friendly rietveld software has wide impact on structure analysis.

Rietveld refinement allows crystallographic analyses to be performed by profile fitting of powder diffraction data. It is widely applied in chemistry, geology, materials science, condensed-matter physics, engineering, and most recently in the life sciences. Use at the NIST neutron source began almost immediately after Hugo Rietveld's seminal paper was published in 1969. The Rietveld technique is of particular value for neutron work, as it offers access to the many advantages of neutron diffraction with short data collection times and without the requirement for large single crystals.

Since the 1970s, three generations of neutron diffraction instrumentation have been built at the NIST Center for Neutron Research (NCNR); the current instrument is the most versatile and highest resolution neutron powder diffractometer in the United States. During this same period, however, development efforts in Rietveld software lagged behind. This changed significantly when the NCNR developed EXPGUI, a software package to aid users of Los Alamos' General Structure Analysis System (GSAS) package. GSAS is considered to be the most sophisticated and powerful Rietveld package, but it has a very dated command-line user interface that hinders potential users. With EXPGUI, users access GSAS via a modern, user-friendly graphical user interface.

The EXPGUI software continues to draw thousands of people to the NIST Web site and to sites in Australia, Canada, and England where the EXPGUI Web pages are mirrored. In the past year alone, the EXPGUI documentation and tutorial Web pages were visited more than 100 000 times and the software was downloaded several thousand times.

For further information, see www.ncnr.nist.gov/xtal.

CONTACT: Brian Toby, [phone]; brian. [e-mail].