Good eveneing, Ioannis Madesis
As you observed yourself: The (primitve) unit cell of your structure does not have enough Cu1 to support AFM on that sublattice. For that you need at least two Cu1 atoms. You achieve that by doubling (at least) the unit cell (perhaps using supercell) and assigning two different numbers to the Cu-sites you want to assign opposite spins to. As far as I recall you should double the unit cell along the a- AND the b-axis to be able to assign the correct spin directions. If you want to describe AF stacking sequences along the c-axis you will have to double the unit cell along that axis. Once you assigned numbers to Cu according to their two spin directions in your supercell (say, leave Cu1 for up, rename the Cu1 you want to point down into Cu3) you can let nn and symmetry do the job of finding the corresponding space group - which will necessarily be different from 123 (consult the UG for this procedure).
Good luck Martin Pieper --- Dr. Martin Pieper Karl-Franzens University Institute of Physics Universitätsplatz 5 A-8010 Graz Austria Tel.: +43-(0)316-380-8564 Am 15.05.2015 14:32, schrieb Madesis Ioannis(John):
Good evening everyone I am having trouble with the struct file for these calculations. To be more specific: This material has 2 nonequivalent Cu atoms, Cu1 and Cu2. Each one of these sits at the four corners of the unit cell, Cu1 at z=0 and Cu2 at approximately z=1/3, and the space group is 123. In order to achieve AFM ordering, I need to have 2 types of Cu1, and the spacegroup doesn't let me do that. Once I place Cu1(up), all 4 corners have Cu1(up). What can I do to solve this?
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