Crystal structure refinement. A crystallographer’s guide to SHELXL / Усовершенствование кристаллической структуры. Руководство для кристаллографов по SHELXL

The 5000 lines of FORTRAN code that became known as SHELX-76 had their origins around 1970 when the University of Cambridge replaced the ICL Titan computer with an IBM-370. My previous attempts to write programs used Titan Autocode, a simple but efficient programming language closer to assembler than to a modern high-level language. With the IBM computer came two major innovations: a FORTRAN compiler and punched cards. Being forced to rewrite my first attempt at a crystallographic least-squares refinement program (called NOSQUARES) in another language was a good opportunity to learn from my mistakes, but—since I was too lazy to read the FORTRAN manual or attend a course—I rewrote the program in a very simple subset of FORTRAN that bore a curious resemblance to Titan Autocode, and avoided features that might have been difficult to port to other computers so that I would never have to rewrite it again. This had the advantage that it produced efficient code, essential in view of the limited speed and memory of the mainframe computers of the time (about 0.0001 times that of current PCs). Actually SHELX-76 still compiles and runs correctly using almost any modern FORTRAN-95 compiler.
At the time I would have regarded myself as an inorganic chemist who was interested in applying a variety of physical methods; the title of my Ph.D. thesis (under the supervision of Evelyn Ebsworth) was ‘NMR Studies of Inorganic Hydrides’. When I moved to the Georg-August University of Göttingen in 1978 I discovered that my German colleagues were so much better at ‘cooking’ (preparative chemistry) than I was that it would be better if I concentrated on crystal structure determination, for which there was a pressing need in order to characterize all the compounds they were synthesizing. <...>