How to plot Fermi Surface

[maomaohu]

Dear All,

I have a question about how to plot a Fermi Surface of copper with the results of the 3D bandstructure calculations? I have read these two related topics http://quantumwise.com/forum/index.php?topic=2391.0#.VFWEDRZ3TbY and http://quantumwise.com/forum/index.php?topic=1885.msg9256#msg9256

So I did this:
1. Generated 50x50x50 k-points in the first Brillouin zone of copper
2. calculated the eigenvalues for those k-points following the band structure calculations in http://quantumwise.com/publications/tutorials/item/107-calculate-the-band-structure-of-a-crystal
3. Arrange the calculated data into a .bxsf file and visualized it by XCRYSDEN, then I got the correct result of the Fermi surface(attached)
4. I tried to do the same thing in MATLAB, so I got the locations of the k-points whose energies lie within Ef+/-0.03231813eV (Ef is the Fermi level), then plotted in MATLAB and got the wrong result as attached pictures. It's an olive-shaped surface, but a nice sphere shape in <111> directions

Is this because the first brillouin zone I plotted in MATLAB is a cubic structure instead of a BCC structure? Or did I do something wrong with getting the k-points? Please help me! Thank you so much for your time!

[Anders Blom]

It's hard to say, since you did the Matlab script yourself. But generally speaking  you need a very dense k-point sampling and then you need to interpolate to E=0. I guess when you select only a subset of points the sampling density becomes too low.

And yes, if you use fractional k-points, it will be distorted, it must be Cartesian.

Note that we are planning to make this kind of plot directly in VNL - soon

[maomaohu]

Thanks a lot, Dr. Blom! Looking forward to the new features!