The phase problem in neutron crystallography.
The straightforward solution of the crystal structure of cyclosporin (C(62)H(111)N(11)O(12).H(2)O) by a modified Shake-and-Bake procedure, using experimental neutron diffraction data alone, shows that the positivity of the density function is not a necessary prerequisite for solving the phase problem. The initial applications suggest the intriguing possibility that positivity may actually be a hindrance.
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