SHELX C/D/E: Difference between revisions

'''SHELXC''' is designed to provide a simple and fast way of setting up the files for the programs '''SHELXD''' (heavy atom location) and '''SHELXE''' (phasing and density modification) for macromolecular phasing by the MAD, SAD, SIR and SIRAS methods. These three programs may be run in batch mode or called from a GUI such as [[CCP4i]] or (better) [[hkl2map]]. SHELXC is much less versatile than the Bruker AXS XPREP program for this purpose, but if you are sure of the space group and there are no problems with the indexing or twinning and the f’ and f” parts of the scattering factors do not need to be refined, SHELXC should be adequate. SHELXC can read either HKL2000 format .sca files or SHELX .hkl files (F-squared unless the -f switch is used to specify F). To transfer data from CCP4 it is advisable to generate .sca files using 'output unmerged polish' from SCALA or to use the program mtz2sca written by Tim Grüne and supplied with SHELX.  The current version of SHELXC outputs extra useful diagnostic statistics if fed unmerged data. SHELXC, SHELXD and SHELXE are stand-alone executables that do not require environment variables or parameter files etc., so all that is needed to install them is to put them in a directory that is in the ‘path’ (e.g. /usr/local/bin or ~/bin under Linux).

which would read the instructions from the file t and write the files xx.hkl (h,k,l,I,sig(I) in SHELX HKLF4 format for density modification by SHELXE), xx_fa.ins (cell, symmetry etc. for heavy atom location using SHELXD) and xx_fa.hkl (h,k,l,FA,sig(FA),alpha for both SHELXD and SHELXE). The starting phases for density modification are estimated as (heavy atom phase + alpha) in the simplified approach used by SHELXE, alpha is calculated by SHELXC from the anomalous and dispersive differences. For SAD alpha is 90º (I+ > I–) or 270º (I+ < I–), for SIR and RIP alpha is 0º or 180º and for SIRAS or MAD alpha may be anywhere in the range 0º to 360º.