[Pw_forum] How does PDOS projection define xyz directions

[Paolo Giannozzi]

On Fri, 2015-01-02 at 10:05 -0600, Sai Kumar Ramadugu wrote:
> Any suggestions for the above post?

http://www.quantum-espresso.org/faq/self-consistency/#6.5

Paolo
> 
> 
> Thanks for your time!
> 
> 
> Regards
> Sai
> 
> 
> 
> 
> ------------------------------
> Sai Ramadugu
> University of Iowa, Iowa City, USA
> 
> On Mon, Dec 29, 2014 at 4:55 PM, Sai Kumar Ramadugu
> <sramadugu at gmail.com> wrote:
>         Dear QE Users,
>         
>         
>         
>         I'm confused about how the projwfc.x does the projection to
>         produce PDOS plots.
>         
>         I'm running the calculations of bulk magnetite Fe3O4. It has
>         two ways to set up the
>         
>         structure: cubic (ibrav = 1, with 56 atoms) cell and hexagonal
>         (ibrav = 4, with 42 
>         
>         
>         atoms) cell. I did PDOS calculation for both of them and
>         checked different d-orbital 
>         
>         
>         components (eg: dz2 and dx2-y2, and t2g: dxy, dxz and dyz) for
>         octahedral Fe. I found 
>         
>         
>         the five different d-orbital distributions are very different
>         for the same type of Fe.
>         
>         
>         The PDOS of different d-orbitals of octahedral Fe in Fe3O4
>         cubic cell shows perfect, 
>         
>         
>         classical textbook-style octahedral crystal field splitting,
>         where dz2 and dx2-y2 are 
>         
>         
>         degenerate and dxy, dxz and dyz are degenerate. And their
>         energy levels also match 
>         
>         
>         theoretical bonding, nonbonding and antibonding model.
>         
>         
>         However, the PDOS of different d-orbitals of octahedral Fe in
>         Fe3O4 hexagonal cell 
>         
>         
>         is much more complicated than the cubic one. None of the
>         d-orbitals are degenerate. 
>         
>         
>         Although I can tell that their total d-orbital distribution
>         must be the same with the one 
>         
>         
>         we got from the cubic cell, the "dz2, dx2-y2, dxy, dxz and
>         dyz" here are NOT the "real 
>         
>         
>         ones" that we expected to see as those in cubic case. For
>         example, a peak that is 
>         
>         
>         supposed to be only contributed by dz2 or dx2-y2 (eg) orbital,
>         is a mixture of all the five 
>         
>         
>         d-orbitals. So now we can't get the correct d-orbital eg and
>         t2g occupancies in 
>         
>         
>         hexagonal cell.
>         
>         
>         
>         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.
>         
>         
>         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 am attaching the figures of pdos calculations for cubic
>         Fe3O4 and hexagonal Fe3O4.
>         
>         
>         Any suggestions are welcome.
>         
>         
>         Thank you,
>         
>         
>         ----------------------------
>         
>         Sai Ramadugu
>         
>         University of Iowa
>         
>         
> 
> 
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222