Dear Shishir, The beq parameter is refered to in the Topas manual as the isotropic temperature factor. Sometimes called a thermal parameter. It is related to the Uiso in some other refinement programs by Uiso = Beq/(8 x pi^2).
In order to control the mixing on two sites within TOPAS you would want to put in something along the lines of: " prm ZnOnZnSite 1 min=0; max=1; prm CuOnZnSite = 1 - ZnOnZnSite; : 0.20509`_0.03706 site Cu num_posns 3 x 0.5 y 0 z 0.5 occ Cu = CuOnCuSite; occ Zn = ZnOnCuSite; beq @ 0.1011 " I have used this in a refinement for refining the Cu:Zn ratio on a site. The prm section defines the names of the occupation parameters and constrains them to total 1 but you will probably want to change this in your refinement. Best regards and good luck Ross Colman P.s. I wouldn't suggest trying to refine Cu:Zn ratios using xray data. I was using this for some powder neutron refinements. sisir ray wrote: > > Dear All, > I am a TOPAS academic user and I was wondering what is the significance of "beq" parameter in the refinement process.In other words how should I change it to get started in refining a structure.As the examples suggest I can get started with 1.But should I change it 0.5 ,If I have two element at one site i.e. for systematic substitutions.Thank You for your help. > Best > Shishir Ray -- ________________________________ Ross Colman G19 Christopher Ingold Laboratories University College London Department of Chemistry 20 Gordon Street London WC1H 0AJ Phone: +44 (0)20 7679 4636 Internal: 24636 Email: ross.col...@ucl.ac.uk > Dear All, > I am a TOPAS academic user and I was wondering what is the significance of > "beq" parameter in the refinement process.In other words how should I > change > it to get started in refining a structure.As the examples suggest I can > get > started with 1.But should I change it 0.5 ,If I have two element at one > site > i.e. for systematic substitutions.Thank You for your help. > Best > Shishir Ray >
