Studying Dirac nodal line with z2pack
Stephanie Mack
samack at berkeley.edu
Thu May 18 02:52:07 CEST 2017
Hello,
I'm a graduate student in Jeff Neaton's group at Berkeley and am currently
using Z2pack to study a few of my systems. It's been going well so far, but
I had a few questions if you would be able to provide some guidance.
One of my systems is a Dirac nodal line and I wanted to compute the Berry
phase using a ring around the nodal line to show it's nontrivial. I can see
how to do it for the case of a single Dirac point with the Sphere in the
shape module, but is that the only shape currently implemented? Is there a
"ring" to use as the shape for line.run()?
The nodal line is in the kz=0 plane, so one thing I've tried so far is
finding the point on the nodal line with a minimal kx value and then
calculating one string around the sphere still using the surface module.
However, I'm not sure how to specify I want the line to be at constant x
and just traverse around the sphere in the y-z directions.
Another idea I was trying was to add a "class" to the shapes.py module for
a ring, just based on the sphere one that's already there, the only
difference being that I don't update the x value. (I realize this is very
system specific and not a general solution). It's not clear to me how
line.py actually iterates around this ring to calculate the wannier charge
centres (and thereby get the Chern number).
Do either of these seem plausible? I could also send my inputs and/or
errors if you want. Although if there's already something implemented I've
missed please let me know...
Lastly, one quick question, would you mind clarifying if the coordinates
for the centre of a sphere should be given in cartesian or direct
coordinates?
Thank you in advance for any feedback!
Best,
Stephanie
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