Refinement constrained-restrained

Konnert, J. H. A restrained-parameter structure-factor least-squares refinement procedure for large asymmetric units. Acta Cryst. A32, 614-617 (1976). Sussman, J. L., and Podjarny, A. D. The use of a constrained-restrained least-squares procedure for the low-resolution refinement of a macromolecule, yeast tRNAfActa Cryst. B39, 495-505 (1983). 

Sussmann, J. L., Holbrook, S. R., Church, G. M., and Kim, S. H. 1977. A structure-factor least-squares refinement procedure for macromolecular structures using constrained and restrained parameters. Acta Cryst. A33 800. 

The use of density functional theory calculations is increasing, and at present such calculations should come with a health warning. Within the set of papers reviewed here there are many examples of structures calculated both ab initio and by density functional theory. The results demonstrate well the unpredictability of density functional theory for molecules which are not very similar to others for which its reliability has already been tested. Bond lengths may be long or short, often by 5 pm or even more, and angles are also potentially in error by 3-5 °. We need to be very careful, therefore, when using only the results of density functional theory calculations to restrain or constrain electron diffraction refine-... 

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