CRUNCH: SOLVING STRUCTURES USING KARLE-HAUPTMAN MATRICES. R.A.G. de Graaff, Leiden Institute of Chemistry, Gorlaeus Laboratories, University of Leiden, PO Box 9502, 2300 RA Leiden, The Netherlands and R. de Gelder, Department of Inorganic Chemistry, Nijmegen SON Research Center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands

Crunch is a system of programs aimed at solving difficult struc-tures by direct methods in a completely automatic way. Phase determination is by construction and concurrent maximization of Karle-Hauptman determinants. Trial models obtained in this way are extended to the complete model by intelligent Fourier recycling.

The Generalized Maximum Determinant Rule states that from all possible sets of phases of the reflections contained in a given Karle-Hauptman matrix, the most probable set maximizes the determinant of this matrix.

Methods of construction of suitable matrices, as well as ways of maximizing the determinant as a function of the phases, have been developed. The program has been very successful in solving the phase problem, even in cases where other, commonly available, programs failed.

The perhaps best known example is the structure put on the Internet by Dr Huffman, which was solved by K. Goubitz and M. Numan of the University of Amsterdam, using Crunch in default settings.

References:

Automatic determination of Crystal Structures using Karle-Hauptman matrices, Acta Cryst A49 (1993), pp 287-293, R. de Gelder, R.A.G. de Graaff & H. Schenk.

IUCr Newsletter Vol. 3 No. 1, page 8.