12.4 Input data

A large percentage of the problems reported to the mailing list are caused by incorrect input data. Before reporting a problem with strange crashes or strange results, please have a look at your structure with XCrySDen. XCrySDen can directly visualize the structure from both PWscf input data:

   xcrysden --pwi "input-data-file"

and from PWscf output as well:

   xcrysden --pwo "output-file".

Unlike most other visualizers, XCrySDen is periodicity-aware: you can easily visualize periodically repeated cells. You are advised to always use XCrySDen to check your input data!

12.4.0.1 Where can I find the crystal structure/atomic positions of XYZ?

The following site contains a lot of crystal structures: http://cst-www.nrl.navy.mil/lattice.
"Since this seems to come up often, I'd like to point out that the American Mineralogist Crystal Structure Database (http://rruff.geo.arizona.edu/AMS/amcsd) is another excellent place to find structures, though you will have to use it in conjunction with the Bilbao crystallography server (http://www.cryst.ehu.es), and have some understanding of space groups and Wyckoff positions". See also: http://cci.lbl.gov/cctbx/index.html.

12.4.0.2 My crystal has a ⁴H²¹_311c x $\sqrt{{\pi }}$ structure, how does this translate to QE input data?

There are several different way to specify structures, described in detail in Doc/INPUT_PW.*.

12.4.0.3 How can I generate a supercell?

If you need to create a supercell and are too lazy to create a small program to translate atoms, you can

• ``use the 'spacegroup' program in EXCITING package (http://exciting-code.org) to generate the supercell, use 'fropho' (http://fropho.sourceforge.net) to check the symmetry'' (Kun Yin, April 2009)
• ``use the PHON code: http://www.homepages.ucl.ac.uk/~ucfbdxa/'' (Eyvaz Isaev, April 2009).

12.4.0.4 Where can I find the Brillouin Zone/high-symmetry points/irreps for XYZ?

"You might find this web site useful: http://www.cryst.ehu.es/cryst/get_kvec.html" (info by Cyrille Barreteau, nov. 2007). Or else: in textbooks, such as e.g. The mathematical theory of symmetry in solids by Bradley and Cracknell.

12.4.0.5 Where can I find Monkhorst-Pack grids of k-points?

Auxiliary code kpoints.x, found in pwtools/ and produced by make tools, generates uniform grids of k-points that are equivalent to Monkhorst-Pack grids.