Note on strengthened translation functions: the positioning of a well oriented molecular fragment using DIRDIF procedures

Strengthened translation functions have been defined [Doesburg & Beurskens (1983). Acta Cryst. A39, 368- 376] as convolutions of two electron density functions: i.e. the electron density representing the known fragment and the electron density obtained by the application of the DIRDIF procedures [Beurskens et al. (1982). In Conformation in Biology, edited by R. Srinivasan & R. H. Sarma. New York: Adenine Press]. Similar translation functions are defined as convolutions of the DIRDIF Fourier map with itself. The new functions are less powerful. The combination of the two types of functions, however, results in a more reliable method for the positioning of a fragment, if the fragment constitutes at least 10% of the total scattering power of the primitive unit cell. Examples of applications to known structures are given.