Improving direct-methods phases by heavy-atom information and solvent flattening

In a recent series of papers, a procedure has been described for phasing all the reflections up to derivative resolution by using triplet phase relationships [Giacovazzo, Cascarano & Zheng (1988). Acta Cryst. A44, 45-51]. The resulting electron-density maps show good correlation with the correct maps but usually are not straightforwardly interpretable. In this paper, the quality of the phases is improved by: (a) exploiting the information on the heavy-atom structure, which becomes available as soon as protein phases are available; (b) applying a suitable solvent-flattening procedure (FLEX), which proves highly effective in reducing the phase error.