SIR2000-N, a program for large and small crystal structures

The program SIR2000 [Burla et al. (2000). Acta Cryst. A56, 451-457] was designed for the ab initio solution of macromolecular crystal structures, provided that the data resolution is no lower than 1.2 Å. As the phasing procedure of SIR2000 is rather time consuming, modifications have been introduced to improve its efficiency and to make it additionally suitable for small molecules (new version SIR2000-N). The role of the tangent refinement in modern phasing procedures is enlightened.