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> In addition to the possibility that the true space group is P6 as > suggested by Eleanor, it could also be P321 or P312, though the latter > is uncommon. Actually, the full list of possibilities is a bit larger. I have no clue how likely the obscure possibilities listed here are though. You find the complete (i hope so at least) list below. possibilities are listed as >From X to Y using: * Z where X would be a candidate 'true' point group Y the 'observed' point group P622 and Z the twin law. Some point groups have funny names such as C 1 2 1 (2*y,-x+y,z). This indicates that the point group is equal to C2, albeit in a somewhat nonstandard setting [Note that C 1 2 1 (x+y,-x+y,z) is not equal to C 1 2 1 (2*y,-x+y,z)]. --------------------------------------------------------------------- >From C 1 2 1 (2*y,-x+y,z) to P 6 2 2 using : * h+k,-h,l >From P 6 to P 6 2 2 using : * -h-k,k,-l >From C 2 2 2 (x+y,2*y,z) to P 6 2 2 using : * -h-k,k,-l >From P 3 2 1 to P 6 2 2 using : * -h,-k,l >From C 2 2 2 (2*x,x+y,z) to P 6 2 2 using : * -h,h+k,-l >From C 1 2 1 (x+y,-x+y,z) to P 6 2 2 using : * h+k,-k,-l >From C 1 2 1 (x+y,2*y,z) to P 6 2 2 using : * -h-k,k,-l >From C 1 2 1 (x-y,2*x,z) to P 6 2 2 using : * h+k,-k,-l >From C 2 2 2 (x-y,x+y,z) to P 6 2 2 using : * -h-k,k,-l >From P 3 1 2 to P 6 2 2 using : * -h-k,k,-l >From C 1 2 1 (2*x,x+y,z) to P 6 2 2 using : * -h,h+k,-l >From C 1 2 1 (x-y,x+y,z) to P 6 2 2 using : * -h-k,k,-l --------------------------------------------------------------------- For those who have interest, please find the full set point groups between P1 and P622 in a graphical representation at http://cci.lbl.gov/~phzwart/p622.png HTH Peter p.s. If you want to know how this image and list was generated, please contact me personally
