additional symmetry restrictions

jggoetze

I am trying to refine atom positions of a zeolite using PXRD data in the Topas GUI.

Right now, for a number of atoms, I get too high values for Np when refining atom positions. I think this is because I don't know how to make Topas follow some additional symmetry restrictions for these atoms.

For instance, for a certain atom position, I want to apply a symmetry restriction such that: x,y,z = x,2x,z. Is it possible to refine the x and y (and z) coordinates of this atom, while keeping y=2x? I tried writing "=2*x" in the Codes field for the y coordinate of this atom, but that doesn't work, because "Uninitialized_Variable in equation: x".

Is there any way of doing this, either in the GUI or in Launch mode?

Thank you in advance!

mw

This should be possible if you use, for example:

site O1 x xO1 0.1 y =2*xO1; :0.2 z 0.9 occ O 1. beq 1

jggoetze

Thank you mw, this works perfectly!