SIMPEL83, A Symbolic Addition Program System for Direct Methods Based on Higher Invariants
The program system SIMPEL83 is a complete direct methods system, which starts from ∣F ∣-values, produces an E-map and finally refines and correct the structure. The unique part of SIMPEL83 is formed by a series of routines, successively gathering the relationships, determining a starting set, carrying out a symbolic addition, finding the correct numerical values for the symbols and executing a numerical phase extension and refinement. The other parts of the program system consist of a normalization program and a Fourier program, peak search and map interpretation program. Usually the latter parts are the same as those used in MULT AN, however, they may also belong to other systems, such as the XRAY or XT AL system or a local system. Our system ends with a very fast diagonal least squares structure factor program, which enables us to check interactively solutions from E-maps and refine structures at minimal computing-costs from R=45% down to R=15%. At present this program AMALS also contains error-recovering routines to delete erroneous atom positions and to introduce missing positions in the model (Shi and Schenk, 1988).
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