[CCP14 Home: (Frames | No Frames)] CCP14 Mirrors: [UK] | [CA] | [US] | [AU]

## Setting atom position constraints in LHPM-Rietica [x, 2x, z sites] (relevant to DBWS, Fullprof, as well)

The CCP14 Homepage is at http://www.ccp14.ac.uk

[Tutorials page] | [LHPM-Rietica Tutorial Index]

 LHPM-Rietica Rietveld (like DBWS and Fullprof Rietvelds) does not automatically handle symmetry constraints. Instead the user must manually implement the symmetry constraints. The following gives an example of how to do this with x, 2x, z positions.

 In the following screen dump, the O1 and O2 atoms are both x, 2x, z positions. To correctly refine the Oxygen atom positions, y must shift double to that of x to satisfy the constraints of symmetry for this particular Titanate structure.

 To set the atom shift constraints via the GUI (Graphical User Interface), first the atom positions must have the refinement flag set (via the Model, Phases menu). Thus the following screen image shows the atom position flags being set to refine for the Oxygens. Note that the 0.25 z position for O1 is not set to refine as this is a special position. You would normally check in the IUCr International Tables as to find out the symmetry constraints of each position.

 To set x, 2x atom constraints, now enter Model, Constraints. Click and drag via the Mouse is now used to set the constraints from the list of refined parameters.

 As an example for O1 (Oxygen 1). Click and drag the P 1: x(O1) from the top-middle box to the bottom left box. Then click and drag the P 1: y(O1) from the top-middle box to the bottom left box. However, we are not finished as this sets a linear 1:1 (x, x, z) constraint on the two parameters whereas we need a 1:2 constraint (x, 2x, z).

 Now, in the bottom right /value box. Set this to 2. This has now set the x, 2x, z constraint.

 Now do the same for the O2 position.

 If you manually peruse the INP input file; you will see the 11/12 code words as the 21/22 codewords that show how these constraints are represented in the input file. (near the bottom of the input file in bold) ```Oxygen Deficient Titanate 0 6 1 -5 0 0 0 0 0 1 0 0 0011100002120010000 0.000 0.000 0.00000 1.54051 1.54433 0.50000 1.00 7.0000 1.0000 0.00 50.0000 0.0000 0.000 300.100.900.900.900.90 15.000 0.025 150.000 0.000 0.000 4 0.000 0.000 -0.047648 0.000 131.700000 -1.085000 0.001540 0.0000E+0 0.0000E+0 0.0000E+0 0.000 0.000 0.000 0.000 0.000 0.000 A new phase 8 1 0.0 0.0 1.0 0.0 0.0 1.0 P 63/M M C BA1 BA 0.00000 0.00000 0.25000 0.60000 0.08333 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 BA2 BA 0.33333 0.66667 0.09104 0.00000 0.16667 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 TI1 TI 0.00000 0.00000 0.00000 0.00000 0.08333 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 FE1 FE 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 TI2 TI 0.33333 0.66667 0.84793 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 FE2 FE 0.33333 0.66667 0.84793 0.00000 0.16667 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 O1 O 0.52066 0.04117 0.25000 0.00000 0.50000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 O2 O 0.83423 0.66846 0.08313 0.00000 0.50000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 2.105470E-04 0.0000 0.00900 0.00680 0.00190 0.00000 5.6925 5.6925 13.9557 90.0000 90.0000120.0000 1.00000 0.00000 0.06624 0.00000 0.54430 0.00250 0.00000 0.00000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 11.000 12.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 21.000 22.000 41.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 31.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 ```

 Now that these atom positions are appropriately constrained, you can refine them.

[Tutorials page] | [LHPM-Rietica Tutorial Index]

 [CCP14 Home: (Frames | No Frames)] CCP14 Mirrors: [UK] | [CA] | [US] | [AU]

If you have any queries or comments, please feel free to contact the CCP14