Section 9.5.2.2. Program system

All calculations were performed on the University of Cambridge IBM 3081 D using the programs BIBSER, CONNSER, RETRIEVE, GEOM78, and PLUTO78 (Allen et al., 1979). A stand-alone program was written to implement the selection criteria, whilst a new program (STATS) was written to perform the statistical calculations described below. It was also necessary to modify CONNSER to improve the precision with which it locates chemical substructures. In particular, the program was altered to permit the location of atoms with specified coordination numbers. This was essential in the case of carbon so that atoms with coordination numbers 2, 3 and 4 (equivalent to formal hybridization states sp¹, sp², sp³) could be distinguished easily and reliably. Considerable care was taken to ensure that the correct molecular fragment was located by GEOM78 in the generation of geometrical tabulations. This often involved the explicit specification of H atoms in fragments, and the extensive use of geometrical tests on valence and torsion angles. Considerable use was also made of chemical structural diagrams, which are available in the Cambridge in-house version of the CSD for some 81% of all entries. Chemical diagrams proved useful, for example, in identifying the various coordination environments commonly adopted by atoms such as As, B, P, etc.