Journal of Applied Crystallography

Volume 46, Part 6 (December 2013)


research papers



J. Appl. Cryst. (2013). 46, 1592-1602    [ doi:10.1107/S0021889813024709 ]

A robust tangent procedure

M. C. Burla, C. Giacovazzo and G. Polidori

Abstract: Third-generation direct methods programs are based on a phasing algorithm (e.g. the tangent or the parameter shift method) and on dual space refinement techniques. The two spaces may be alternated during the phasing procedure or used in a sequential way: for example, first phase and after extend and refine. The tangent approach in SIR2011 belongs to the second category: phases are first estimated by the tangent formula, then their extension and refinement is performed in direct space via electron density modification techniques. In this article a number of new algorithms are described, with the aim of improving the SIR2011 tangent step and allowing more efficient phase extension and refinement. New criteria were chosen for defining the number of reflections to phase, for modifying the tangent weighting scheme, and for fixing the active use of the psi-0 triplets and of the quartet invariants. Each tangent trial may now be submitted to the RELAX procedure, a tool for moving to the correct position a well oriented but misplaced structural model. The resulting procedure shows surprising efficiency, testified by a wide set of applications. The experimental results have been compared with the tangent and VLD (vive la différence) approaches implemented in SIR2011.

Keywords: structure solution; SIR2011.


pdfdisplay filedownload file

Portable Document Format (PDF) file
[ doi:10.1107/S0021889813024709/he5618sup1.pdf ]
Supplementary tables


Notes:

To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.

The download button will force most browsers to prompt for a file name to store the data on your hard disk.

Where possible, images are represented by thumbnails.

 bibliographic record in  format

  Find reference:   Volume   Page   
  Search:     From   to      Advanced search

Copyright © International Union of Crystallography
IUCr Webmaster