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Band Structure

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Julien Steffen edited this page Mar 20, 2024 · 1 revision

For a band structure calculation, a high-quality single point (see here or a DOS (see here) calculation needs to be done first. The only change/addition is that the CHGCAR file needs to be printed out! Add the line LCHARG = .TRUE. to the INCAR file.

After the calculation has been made, copy the CHGCAR file (and the input) to a new folder and add the following keywords to the INCAR file:

  • ICHARG = 11 Density will be kept fix, no self-consistency!
  • ISMEAR = 0 Gaussian smearing, tetrahedron smearing cannot be used for band structures!
  • SIGMA = 0.01 Small value needed

Further, the KPOINTS file must be edited, since now only a 1D path through the reciprocal space shall be sampled. Such a path can either be set up by knowledge or with the xcrysden program (obtain it from here).

In order to use xcysten, the POSCAR file of the system of interest must be converted to an xsf-file. In order to do this, download the v2xsf program from the respective github page. Execute the program:

v2xsf POSCAR

With this, a compressed file POSCAR.xsf.gz will be generated. Start the xcrysden program with the command:

xcrysden

and open the compressed xsf-file with File -> Open Structure -> Open XSF. After opening, go to Tools -> k-path Selection. In the new window, you can select points of high symmetry. Their reciprocal coordinates will directly be written on the right side. You then either copy them manually or export them to a name.kpf file.

Finally, the KPOINTS file should look something like this:

 K-points
 30
line-mode
fractional
0.0  0.0  0.0   Gam
0.5  0.0  0.0   X

0.5  0.0  0.0   X
0.0 -0.5  0.0   M

0.5 -0.5  0.0   M
0.0  0.0  0.0   Z

0.0  0.0  0.5   Z
0.0  0.0  0.0   Gam

In this file, two coordinates written in lines without empty line between them are always connected with a one-dimensional path for integration. If the single paths shall be connected, the coordinates of the first point in the second block must be the same as of the second point of the first point, and so forth. The number in the second line of the KPOINTS file (30 in this case) determines on how many points along one single line the band energies shall be calculated.

After the calculation is finished, open p4v in the results folder and go to DOS+bands -> Show -> DOS (or DOS and Bands)

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