  A new method for solving small X-ray structures with up to couple of hundreds
of atoms in the unit cell has been developed. The method works by locating
atoms one-by-one via global minimization of a newly defined single-atom R1
factor in real-space. In total forty test cases (of twenty samples), every
resulting model has at least 52% atoms located correctly, and in more than half
of the cases this percentage is 90% and higher. For most
heavier-atoms-containing (heavier than Si) small structures it is sufficient to
use a single-solution strategy (using the as-collected reflection intensities).
But for most lighter-atoms-only (C, N, O and F) small structures it is
necessary to try multi-solution strategy: try different B values for modifying
the reflection intensities by multiplying them with exp(B s2) before feeding to
the method, where s = sin{\theta}/{\lambda}, and pick the best solution. This
method has been demonstrated to be very effective for locating heavier atoms,
so, it has potential applications in macromolecular crystallography by
assisting determination of heavy-atom substructures.
