SHELXL-93 is general and efficient for all space groups in all settings and there are no arbitrary limits to the size of problems which can be handled, except for the total memory available to the program. All instructions are in machine independent free format, with extensive use of default settings to minimize the amount of input required from the user. Instructions and data are taken from two standard (ASCII) text files, so that input files can easily be transferred between different computers. SHELXL-93 is provided in source form as well as precompiled PC versions. An application form is reproduced in Appendix F.
The program is available free to academics (and for a modest license fee to commercial institutions) subject to the condition that it is acknowledged in all publications which report structures refined with it.
SHELXL-93 has been designed particularly for optimum performance on computers with vector and pipelined architectures, and most vectorizing compilers achieve a high degree of vectorization for all important routines without special action on the part of the user. The rate-determining routines are provided in a separate file so that they may be compiled with full optimization; it may well prove counter-productive to optimize or vectorize the rest of the program! The distribution and installation of the program is discussed further in Appendix E.
Two auxiliary programs are provided for use with SHELXL-93. PDBINS reads a PDB-format file for a protein and interactively generates a SHELXL-93 '.ins' input file, and CIFTAB reads the '.cif' output file from SHELXL-93 and produces various tables. Users are encouraged to adapt CIFTAB and PDBINS to local circumstances. PDBINS and CIFTAB are described in Appendices B and C respectively.
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