Multiple samplings of the reciprocal lattice and map averaging as a source of phase information.
Presented at the IUCr meeting, Glasgow, 1999.
Abstract
Multiple-crystal averaging has been applied with great success to the
problem of phase improvement, and multiple crystal forms hold
potential as a source of ab-initio phase information. In theory, if
the magnitudes of the continuous molecular tranform are available,
then direct phasing is trivial either in real or reciprocal space. In
practice, the molecular transform is obfuscated by both symmetry and
coarse sampling, thus in general techniques are currently limited to
phase improvement. However phasing a small molecule has been
demonstrated from a single atomic position using 6 copies of the
molecule across 3 crystal forms.
In practice the use of frozen crystals is now a common source of
slightly non-isomorphous crystal forms, which are in some cases useful
as a source of phase information. Trials with simulated data
demonstrate the usefulness of this apprach and the limits arising from
noise in the data and non-isomorphism in the crystals.
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