SHELX makes an impact

The recent release of Thomson Reuters' Journal Citation Report for 2009, reporting an impressive impact factor of 49.9 for Acta Crystallographica Section A: Foundations of Crystallography, has excited much comment amongst crystallographers. The primary cause of this high impact factor is a single feature article by George Sheldrick, A short history of SHELX [Acta Cryst. (2008). A64, 112-122]. Published in a special issue to celebrate 60 years of Acta Crystallographica and the IUCr, it gives an account of the development of the SHELX system of computer programs from 1976 to date.

The article has provided the crystallographic community with a citable reference when one or more of the programs, amongst the most widely used in structure determination, are employed in the course of a crystal structure study. Most citations have been made by small-molecule crystallographers, but citations have also come from articles reporting the structure of biological macromolecules.

Until the publication of this article, the programs in the SHELX package were typically referenced by citing the unpublished computer programs themselves. The total number of citations in the Thomson Reuters statistics (6653 by the end of June 2009 - by any measure a significant achievement) is, of course, dwarfed when the total number of articles that have cited the unpublished programs is considered. A search of Crystallography Journals Online shows that over the years more than 43,000 articles published in IUCr Journals alone have referenced SHELX programs.

This article and its citations will be considered in the impact factor calculation for Acta Crystallographica Section A this year and next year. The journal impact factor that will be reported in 2012 is therefore likely to return to a more normal level of about 2.0-2.5.