sumo-bandstats¶

sumo-bandstats is a program for extracting band gaps and effective masses from a band structure calculation.

Usage¶

The full range of options supported by sumo-bandstats are detailed in the Command-Line Interface section, and be can be accessed using the command:

sumo-bandstats -h

To extract band structure information, simply run the following command in a folder containing a vasprun.xml or vasprun.xml.gz file, which has been calculated along a high-symmetry path:

sumo-bandstats

For example, if we run this command in the sumo/tests/data/Cs2SnI6/bandstructure directory, the output should look like:

Direct band gap: 0.712 eV
  k-point: [0.00, 0.00, 0.00]
  k-point indexes: 0, 113
  Band indexes: 34, 37

Valence band maximum:
  Energy: 1.444 eV
  k-point: [0.00, 0.00, 0.00]
  k-point location: \Gamma
  k-point indexes: 0, 113
  Band indexes: 34, 35, 36

Conduction band minimum:
  Energy: 2.155 eV
  k-point: [0.00, 0.00, 0.00]
  k-point location: \Gamma
  k-point indexes: 0, 113
  Band indexes: 37

Using parabolic fitting of the band edges

Hole effective masses:
  m_h: -0.641 | band 34 | [0.00, 0.00, 0.00] (\Gamma) -> [0.50, 0.50, 0.50] (L)
  m_h: -0.516 | band 34 | [0.00, 0.00, 0.00] (\Gamma) -> [0.50, 0.00, 0.50] (X)
  m_h: -0.641 | band 35 | [0.00, 0.00, 0.00] (\Gamma) -> [0.50, 0.50, 0.50] (L)
  m_h: -0.516 | band 35 | [0.00, 0.00, 0.00] (\Gamma) -> [0.50, 0.00, 0.50] (X)
  m_h: -1.234 | band 36 | [0.00, 0.00, 0.00] (\Gamma) -> [0.50, 0.50, 0.50] (L)
  m_h: -15.158 | band 36 | [0.00, 0.00, 0.00] (\Gamma) -> [0.50, 0.00, 0.50] (X)

Electron effective masses:
  m_e: 0.207 | band 37 | [0.00, 0.00, 0.00] (\Gamma) -> [0.50, 0.50, 0.50] (L)
  m_e: 0.211 | band 37 | [0.00, 0.00, 0.00] (\Gamma) -> [0.50, 0.00, 0.50] (X)

The effective masses are given in units of electron rest mass, \(m_0\).

If we compare this output to the band structure:

We can see that the valence band maximum is composed of three degenerate two-electron bands, whereas the conduction band minimum is composed of a single two-electron band.

The effective masses from \(\Gamma\) to L and from \(\Gamma\) to X are generally small, except for the very flat valence band from \(\Gamma\) to X, which results in masses greater than 15 \(m_0\).

File Searching¶

sumo-bandstats will automatically look for vasprun.xml or vasprun.xml.gz files in the current directory. If the band structure has been broken up into multiple parts (as is common for hybrid band structure calculations), these files will be preferentially used. For this to work, the folders should be named split-0* and sumo-bandstats should be run in the folder containing the splits. For example, if the file structure is as follows:

bandstructure/
    split-01/
        KPOINTS
        vasprun.xml
    split-02/
        KPOINTS
        vasprun.xml

sumo-bandstats should be run in the bandstructure directory.

Basic Options¶

To specify a particular vasprun.xml to extract information from, the --filenames option can be used. If multiple vasprun.xml files are provided, they will be combined into a single band structure.

By default, sumo-bandstats uses parabolic fitting to determine the effective masses. If then --nonparabolic option is used, then non-parabolic fitting of the band edges will be performed.

sumo-bandstats samples 3 k-points when determining the effective masses. This number can be controlled using the --sample-points option.

Command-Line Interface¶

bandstats provides information on the band gap and effective masses of semiconductors.

usage: sumo-bandstats [-h] [-f F [F ...]] [-n] [-s N]

Named Arguments¶

-f, --filenames

one or more vasprun.xml files to plot

-n, --nonparabolic

use a nonparabolic model to fit the effective masses

Default: True

-s, --sample-points

number of k-points to sample in fitting

Default: 3

Author: Alex Ganose Version: 1.0 Last updated: March 4, 2018