yurijanssen
Hi there,
Relatively new to topas, I have been using rigid bodies for my refinement problem. To place my z-matrix-defined rigid body correctly, besides a correct translation vector, I also need to have rotation angles. I think topas defines them around lattice axes a, b, and c. But in what order do these rotations take place?
Is it ABC, CBA or otherwise?
I can find correct angles using simulated annealing, but I would like to be able to do this 'by hand', as well. At this point, I am not clear what my refined angles mean, exactly.
On a side note: it seems to me that having three angles, rather than two, seems more than necessary?
Thanks in advance,
Yuri Janssen
alancoelho
Technical_Reference.PDF explains the 'rotate' keyword; ie.
"rotate rotates point_for_site’s an amount as defined by the rotate E equation around the vector defined by the Cartesian vector qx, qy, qz. The vector can be defined in fractional coordinates using qa, qb and qc instead."
If there's more than one 'rotate' operation then they are processed in the order of appearance.
yurijanssen
Thank you Alan, I should have studied the Topas.inc file a bit more. There the Rotate_about_axies macro is given, and it gives the order of rotations.
Yuri