advantages of upgrading to SHELXL-2014

The advantages of upgrading from SHELXL-97 to SHELXL-2014/7 or later versions

(a) Automatic inclusion of the .res, .hkl and .fab data in the CIF relieves users of having to worry about such things at all and eliminates the need to upload the corresponding structure factor .fcf files. Thus archiving, whether with a paper submitted to the IUCr, or to another journal or to the CCDC is simplified and consistent.

(b) Improved PLATON SQUEEZE procedure. Important and advantageous improvements in the SQUEEZE procedure need SHELXL-2014. The contribution of the solvent region is now stored in the .fab file, thereby keeping the original .hkl files unaltered. This can be useful for anyone wishing to investigate the structure further at some other time. The previous method of using SQUEEZE with SHELXL-97 modified the input .hkl file itself, which is less desirable. The estimated electron count is much more accurate now, because missing reflection intensities are estimated in the calculations (free lunch algorithm as used in SHELXT).

(c) Some improvements in restraints (e.g. RIGU).

(d) Some little-known errors in SHELXL-97 removed (e.g. TWIN with an explicit matrix on the line, even if just the default inversion operation, erroneously puts 0.00 as the Flack parameter in the CIF, even if BASF is not zero).

(e) Improved information content in the CIF, such as the actual space group symbol, proper automatic calculation of completeness at the theta_full and theta_max levels. Correction of the improper filling out of Tmin/Tmax when SIZE was specified (these now go under different CIF names). Thus, less need to hand-edit CIFs.

(f) The ability to refine much larger structures without having to recompile or have the shelxh version. Command line flags facilitate this.

(g) Improvements in the way s.u. values are estimated for noncentrosymmetric structures, thus avoiding the question of whether or not one should merge Friedels in light-atom structures.

(h) Improvements in the precision of the Flack parameter through implementation of Parson's quotient calculations.

(i) Improvements/simplifications for using neutron data.

(j) Improvements in the blank HTAB instruction for generating the needed HTAB instructions automatically for later use.

(k) If a previous refinement has been carried out using SHELXL-97, it is relatively trivial to repeat the final refinement just one more time. Identical results will be obtained with the new version when using the old .ins file, with the exception that the default distance on SIMU has changed and an explicit distance of 1.7 has to be specified on that instruction, when used, to reproduce the old results. The benefits given above outweigh the trivial amount of extra work. Only in the case where SQUEEZE was used previously would a little more work be needed, because one would have to go back to the pre-SQUEEZE .hkl file (this can be recovered from the SQUEEZEd .hkl file with 'platon -z9 name.hkl'). However, as SQUEEZE results generated a few years ago can be inferior to those carried out with the current version of SQUEEZE, a new application of SQUEEZE and final refinement would be preferable in any case.

(l) Installing SHELXL-2014 or later versions is trivial. The executables for Windows-PC, Mac and Linux are freely available from the author at http://shelx.uni-goettingen.de and need no special installation steps or knowledge.

One should not underestimate the advantages of the newer versions doing many things automatically, particularly for users who are not dedicated experts and want a compliant CIF with the minimum of fuss and effort.

See also

New features added to the refinement program SHELXL since 2008 are described and explained in the paper Crystal structure refinement with SHELXL [G. M. Sheldrick (2015). Acta Cryst. C71, 3–8].