Acta Crystallographica Section A

Foundations of Crystallography

Volume 64, Part 2 (March 2008)

short communications

Acta Cryst. (2008). A64, 341-344 [ doi:10.1107/S0108767307067372 ]

Why phase errors affect the electron function more than amplitude errors

E. Lattman and D. DeRosier

Abstract: If Fexp(i) are the set of structure factors for a structure f, the amplitudes can be converted to those of an uncorrelated structure g (amplitude swapping) by multiplying each F by the positive number G/F. Correspondingly, the image f is convoluted with k, the Fourier transform of G/F; k has a large peak at the origin, so that f * k ~ f. For swapped phases, the image f is convoluted with l, the Fourier transform of exp(i [Delta] [alpha] ), where [Delta] [alpha] , the phase difference between F and G, is a random variable; l does not have a large peak at the origin, so that f * l does not resemble f. The paper provides quantitative descriptions of these arguments.

Keywords: phase error; phase swapping.