Dear all,

I have defined a rigid body containing a mixed occupancy site, i.e., two sites 
with the same coordinates and complementary occupancy. When I match up the 
rigid body to my phase it only locks one of the mixed sites to the rigid unit, 
even though both sites are defined in the rigid body XYZ file and also on the 
Atoms tab for the phase. This would be fine if I could constrain the 
x/y/z/Uiso/Frac parameters of the uncaptured site to the captured one, but the 
usual constraints one would apply to a mixed site don't seem to work - so if I 
refine the rigid body angle the uncaptured atom doesn't move with its partner, 
regardless of the combination of refine flags I set on the Atoms tab (and 
certain combinations cause GSAS2 to warn that constrained parameters are not 
being refined together).

Can anyone advise how to achieve mixed occupancy in a rigid body? I don't mind 
whether the solution involves constraints or including both sites in the rigid 

Thanks in advance,

Dr Josie Auckett
Postdoctoral Researcher
Australian Centre for Neutron Scattering
Australian Nuclear Science and Technology Organisation

+61 2 9717 3601<>


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