The phase problem in neutron crystallography

The straightforward solution of the crystal structure of cyclosporin (C₆₂H₁₁₁N₁₁O₁₂·H₂O) 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.