Ab initio structure determinations by direct-space methods: tests of low-density elimination

The low-density elimination method, which was developed for phase extension and refinement, has been investigated regarding its power to solve crystal structures starting from completely random phase sets. The method employs a multi-solution strategy. Low-symmetry structures are easily solvable where phase restrictions are only applied to a few reflections. Even with high-symmetry structures, a reasonable solution was obtained regarding centric reflections as general reflections. It is also shown that the structure of a small protein ribonuclease Ap1 is solvable if the positions of the five S atoms in the protein are known.