[Pw_forum] How does PDOS projection define xyz directions

[Sai Kumar Ramadugu]

Any suggestions for the above post?

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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