Simple structure coordinate input format

[Anna Kuznetsova]

Dear developers and user,

I have to input coordinates of various SiC Polytypes knowing just the sequence of ABC layers in the  unit cell.  What is the simplest input format to provide minimum required parameters (only atoms and their coordinates in the unit cell) to create a structure in VESTA? I could use the menu in VESTA for doing this, but I need to input too many atoms in each unit cell, so wanted to automatize my input.

Thank you for help!

Anna

[Philip Howie]

Dear Anna,

I'm assuming from your question that you'd prefer to specify atom positions in fractional coordinates.  If this is the case, I recommend using the .xtl format.  I attach such a file to generate the C15 Laves phase structure of MgCu2, which should be fairly self-explanatory.

I would also point out that in many cases, exploiting the symmetry operations in the crystal can greatly cut down the number of atoms you need to specify.  In the case of MgCu2, only two atoms need be listed, along with the space group 227.

Hope that helps,

Phil

[Natalia Mazur]

Dear Phil

Currently I'm struggling with similar problem. Could you please tell me what program did you use to create the .xtl file. I've tried excel but when I finally manage to open it in Vesta no atoms are showing and editing your document isn't helping as it always is saved in a different format.

Thanks in advance for your help

Natalia

[Philip Howie]

Dear Natalia,

It should be possible to edit the .xtl file in any text editor, as long as you make sure the filename ends in .xtl when you save it.

If you really want to modify the file in Excel, you'll need to open it as a delimited text file, choosing 'Space' as the delimiter.  Modify the lattice parameters and atomic coordinates as appropriate, then 'Save As...' the file type 'Text (Tab delimited) (.txt)'.  Rename the file, swapping its .txt extension for .xtl and it should open just fine in VESTA.

The real advantage of using the .xtl format is that it's uncluttered and regular enough that one could write a simple script to input the atomic coordinates automatically, without having to go through VESTA's GUI each time - as requested by the original questioner.

Phil

[M. Mushtaq]

Dear Philip,

Thank you so much for uploading this .xtl file. Could we mention lattice vectors in the form of a=ax,ay,az etc, if angles are not 90 degrees in this file, and still to been seen in VESTA?