Relaxation of the resolution requirements for direct-methods phasing.

Shake-and-bake phasing methods have permitted the ab initio solution of crystal structures containing more than 1000 independent non-H light atoms (C, N, O). The success of these procedures is critically dependent upon having diffraction data measured to at least 1.2 Å resolution. A new target function R(2)(φ(h)) is introduced into the shake-and-bake procedure along with a real difference map strategy whereby this resolution limit can be appreciably lowered toward 1.5 Å. These improvements, when applied to moderately high resolution data, may now allow one the possibility to solve structures that are twice as large as could have been solved previously.