[Wien] AFM calculations for YBCO6

[pieper]

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?