[GSAS-II] Refining 2D layered materials

[Dylan J Bardgett]

Dear all,

I am trying to perform Le Bail fits and eventually rietveld refinements 
on layered 2D heterostructure with known orientations to the substrate. 
More specifically, my samples are all oriented such that the 001 axis is 
aligned with the silicon substrate. The diffraction patterns were 
collected on a lab diffractometer oriented such that only (hk0) 
reflections will be observed. I have tried experimenting with the 
preferred orientation parameters, but I get a "Refinement error: invalid 
metric tensor, cell/Dij refinement not advised" error whenever I try to 
refine the unit cell with a non-unity March-Dollase ratio. I haven't 
been able to find any tutorials on refining layered materials in 
GSAS-II. Does anyone have any suggestions?

Best,

Dylan