Advances in the VLD algorithm

The VLD algorithm relies on the properties of the difference Fourier synthesis and is designed for solving crystal structures in the correct space group, starting from random models. The standard approach has been modified by integrating it with the RELAX procedure, for translating to the correct position misplaced but correctly oriented models. A better control of the parameters and additional phase refinement cycles were able to improve the quality of the solutions and to make superfluous, for macromolecules and medium-sized molecules, the least- squares refinement cycles that, in the standard VLD approach, follow the phasing step. As a result, the efficiency of the new VLD algorithm is strongly increased; it has been checked using a wide variety of practical cases and compared with the effectiveness of direct methods.