Novel phasing method using the origin-free modulus sum function expressed in terms of the absolute electron density.

The origin-free modulus sum function SM refines the set Φ of phases of the structure factors by maximizing the coincidence between the experimental origin-free modulus function and the calculated one in terms of the ρ(Φ)2 density function [Rius, J. (1993). Acta Cryst. A49, 406-409]. Maximization is normally achieved through the recursive application of a Fourier-based algorithm. The purpose of the present study is: (i) to show that ρ(Φ)2 can be replaced by |ρ(Φ)| in SM; (ii) to illustrate the viability of the corresponding phasing algorithm with experimental data.