On the computation of structure factors by FFT techniques

The method of structure-factor calculation by fast Fourier transform techniques [Ten Eyck (1977). Acta Cryst. A33, 486-492] is here reviewed. It is found that the recommended sampling of three times the highest index in each direction [Lipson & Cochran (1966). The Determination of Crystal Structures, 3rd ed., pp. 94-102. Ithaca: Cornell University Press] is appropriate for any resolution, provided an adequate Gaussian dampening factor is used. A rule is given to determine this factor.