Direct space methods of structure determination from powder diffraction: principles, guidelines and perspectives

In the last twenty five years structure determination from powder diffraction has evolved from a complex, time-consuming method to one easily usable. While the use of direct methods is restricted to samples well crystallized (sharp peaks, high resolution diffraction), structure solution using global optimization in direct space have become extremely popular, using either publicly or commercially available software. In this article we present a short history of direct space methods of structure determination from powder diffraction, and a list of available software. We then give an overview of frequent issues when solving structures in direct space, as well as how algorithms are currently evolving to solve more complex structures.