Upgrading the twin variables algorithm for large structures

• Published in: Acta crystallographica. Section A, Foundations of crystallography Vol. 56; no. 2; pp. 105 - 111
• Main Authors: Bethanis, K., Tzamalis, P., Hountas, A., Mishnev, A. F, Tsoucaris, G.
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England Munksgaard International Publishers 01.03.2000; Blackwell
• Subjects: Algorithms; Biological compounds; Condensed matter: structure, mechanical and thermal properties; Crystallography, X-Ray; Exact sciences and technology; Organic compounds; Physics; Protein Conformation; Proteins - chemistry; Single-crystal and powder diffraction; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Thermodynamics; Twin variables algorithm; X-ray diffraction and scattering; Direct method; Proteins; Biological compound; Algorithms; Macromolecules; Structure resolution; Refinement; Theoretical study; XRD; Amplitude phase; Resolution; Crystal structure
• ISSN: 0108-7673; 1600-5724
• DOI: 10.1107/S0108767399013355

Phase extension from lower to higher resolution by using an upgraded TWIN variables algorithm [Hountas & Tsoucaris (1995). Acta Cryst. A51, 754–763] in protein molecules with close to 1000 non‐H atoms is presented. Three points of this procedure are of particular interest. (i) The use of a set of auxiliary variables providing a satisfactory fit for many kinds of constraints: the new algorithm works efficiently despite the extreme `dilution' of very limited initial phase information into a much larger set of auxiliary variables. (ii) The extension of this auxiliary variables set beyond the resolution of the observed data, which enhances the phase extension in a so‐called `super‐resolution' sphere. (iii) The use of the crystallographic symmetry as a new figure of merit and as a reliable test for the correctness of the phase‐extension process allows an efficient screening.