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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