CrystalDiffract lets you edit a crystal structure (for a selected, simulated powder pattern). Unlike earlier versions of the software, you now have complete control over all aspects of the structure:
Do the following:
Select the diffraction pattern whose crystal structure you wish to edit. (To do this, locate the pattern's name in the Patterns list and click on it so that the row is shown highlighted. Note that only one pattern may be edited at a time.)
Choose: Edit > Crystal Structure. The crystal editor window (or sheet, on the Mac) appears.
Make any changes you require, then click the window's OK button to recalculate the crystal structure and its corresponding diffraction pattern.
You should enter your spacegroup symbol in plain-text form, with spaces between the symmetry operators, e.g.,
Spacegroup Symbol | CrystalDiffract symbol |
---|---|
P 1 | P -1 |
P m | P m |
P a 3 | P a -3 |
P 2 2 21 | P 2 2 21 |
P n m a | P n m a |
R 3 c | R -3 c |
C 2/c | C 2/c |
I 41/a | I 41/a |
I 41 21 2 | I 41 21 2 |
P 42/m n m | P 42/m n m |
I a 3 d | I a -3 d |
Alternatively, you can specify the spacegroup number.
If your spacegroup is a dual-origin spacegroup, choose the appropriate origin setting using the popup menu on the right-hand side of the Spacegroup field.
To specify Rhombohedral axes for a Trigonal spacegroup, verify the lattice parameter fields so that α = β = γ = 90°. To specify hexagonal axes, ensure that α = β = 90°; γ = 120°.
Enter your lattice parameters, a, b, c (in Å units) and α, β, γ (in degrees).
A scrolling list shows all sites in the crystal's asymmetric unit (not the full unit cell). Use the + or - buttons to add or remove sites. You can rearrange the table by dragging-and-dropping individual rows.
For identification purposes, ensure that each site has a unique site label (alphanumeric characters only).
You must specify the site occupancy: this tells CrystalDiffract which element(s) reside on the site, so that the appropriate atomic scattering factor(s) can be used during intensity calculations.
You can have multiple occupants per site (e.g., Si0.7Al0.2Ti0.1) but the total occupancy must not exceed 1.
If you want to indicate a disordered site (e.g., 50% Al, 50% Si), define a single site, and enter a mixed-occupancy string (e.g., you would enter "Al 0.5 Si 0.5"). Note that this is faster, more elegant - and improves application performance - compared to defining separate sites for each element symbol!
Specify the position of the site in the unit cell using fractional coordinates. You can enter real numbers or fractions (e.g., "0.25" or "1/4" are acceptable).
You may also define atomic displacement parameters, but please take great care to ensure that your values are valid.
See Also