[Pw_forum] How does PDOS projection define xyz directions

[Gabriele Sclauzero]

> I'm thinking why different cell type can make such big difference in PDOS distributions. 
> 
> I guess the "x, y, z" directions defined by projwfc.x in PDOS projection is "cell vector-
> 
> dependent". In cubic Fe3O4, all the six Fe-O bonds around octahedral Fe are parallel 
> 
> to one of the a, b and c cell vectors. So the "x, y, z" in PDOS projection happen to be the 
> 
> same with the "x, y, z" in Fe crystal field splitting. But in hexagonal Fe3O4, all of the 
> 
> octahedral Fe-O bonds are off the cell vectors. So the default "x, y, z" in projection are no 
> 
> longer the same as those that we are looking for on octahedral Fe sites.
> 
> 

Your explanation is somehow right. The spherical harmonics are built in a standard way.
So, for instance, d_xz is “mainly” in the xz plain, etc.
Now, the unit cell itself has an orientation in this Cartesian frame of reference (xyz), which you can see in the output (and is also described here http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idp82000 ).
The easiest thing to do is to use ibrav=0 and specify the crystal axes such that the unit cell has the desired orientation.
Namely, the crystal (or better, the bonds) must have the same orientation (w.r.t. this Cartesian f.o.r.) as in the cubic cell in order to obtain the “correct” PDOS.
> 
> So now I'm thinking how to change the way the projwfc.x does the projection. Because 
> 
> Fe3O4 is just a test for us. We are actually focusing on hematite Fe2O3, which can only 
> 
> be presented by hexagonal (or rhombohedral) cell where all the Fe-O are off the cell 
> 
> vectors. I found that there is something wrong with the eg and t2g PDOS but don't know 
> 
> how to correct it. There seems to be a file called ".../flib/ylmr2.f90". Is this the one 
> 
> controlling projection directions? Or is there any other way that we can let projwfc.x does 
> 
> the PDOS projection along the directions that we really want?
> 
I have a modified version of projwfc.x that allows the user to specify the orientation of the Cartesian frame of reference used to build the spherical harmonics, but I have not yet made it public.
In this simple case it’s enough to rotate the cell using ibrav=0, so I would suggest to try this solution first.

HTH

GS


> Sai Ramadugu
> 
> University of Iowa
> 
> <mag_pdos_hex.png><mag_pdos_cub.png>_______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum


Dr. Gabriele Sclauzero
Materials Theory (D_MATL)
ETH Zurich, HIT G 43.2
Wolfgang-Pauli-Str. 27
8093 Zürich, Switzerland

Phone +41 44 633 94 10
Fax +41 44 633 14 59
gabriele.sclauzero at mat.ethz.ch
www.theory.mat.ethz.ch/people/postdocs/gsclauze

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150106/f85aab8c/attachment.html>