easyunfold is intended for obtaining the effective band structure of a supercell for a certain k-point
path of the primitive cell. It was originally based on
PyVaspwfc for reading VASP wavefunction outputs,
with a notable improvement being that symmetry-breaking is properly accounted for by sampling necessary
additional k-points and averaging accordingly. Documentation site
here!
Our goal is to implement the band structure unfolding workflow in a robust and user-friendly software package. Typical applications of band structure unfolding are the electronic structure analysis of defects, disorder, alloys, surfaces (and more), as illustrated in the example outputs below and docs examples.
For the methodology of supercell band unfolding, see here.
| Cs₂(Sn/Ti)Br₆ Vacancy-Ordered Perovskite Alloys | Oxygen Vacancy (Vₒ⁰) in MgO |
|---|---|
 |
 |
See the easyunfold YouTube tutorial for a quick overview of the theory of band structure unfolding, and a walkthrough of the calculation & analysis workflow with easyunfold.
To generate an unfolded band structure, one typically needs to perform the following steps:
- Create a primitive unit cell, and generate a band structure k-point path corresponding to this primitive cell.
- Create a supercell (e.g. disordered, defective, surface slab etc.), and obtain its optimised structure.
- Generate a series of k-points for the supercell to be calculated.
- Perform a band structure calculation with the supercell, and save its wavefunction output to file.
- Post-process the supercell wavefunction to obtain the unfolded band structure in the k-point path of the primitive unit cell.
These generation and analysis steps are automated in easyunfold, with only the primitive unit cell and
supercell structures required as inputs from the user.
Typically, the supercell comprises some form of symmetry-breaking relative to the primitive cell, such as defects, disorder (e.g. special quasi-random structures (SQS) for site disorder – other forms of disorder such as magnetic, dynamic/vibrational, polar, elastic etc. also possible), or a surface/interface slab. In all cases, the supercell symmetry is lowered compared to the pristine primitive cell. Hence, for a given k-point path in the primitive cell Brillouin Zone, additional k-points are required to be sampled for the supercell, and the extracted spectral weights need to be appropriately averaged to obtain the correct effective band structure (EBS). See the docs Theory page for more details.
Please see the documentation for guides and examples.
easyunfold can be installed from pip:
pip install easyunfold
This will also install the package dependencies, if any are missing.
After installation, running easyunfold on the command-line should give the following output:
Usage: easyunfold [OPTIONS] COMMAND [ARGS]...
Tool for performing band unfolding
Options:
--help Show this message and exit.
Commands:
generate Generate the kpoints for sampling the supercell
unfold Perform unfolding and plotting
A recent version of pip is needed to do this, due to the new style of the pyproject.toml configuration
file.
To upgrade your pip, do:
pip install -U pip
Assuming the package is in the easyunfold folder, use the following command to install:
pip install "./easyunfold[test,doc,pre-commit]"
which also installs additional dependencies for building documentation (doc), running tests (test) and
dependencies for using pre-commit hooks (pre-commit).
If you use easyunfold in your work, please cite:
- B. Zhu, S. R. Kavanagh & D. O. Scanlon, (2024). easyunfold: A Python package for unfolding electronic band structures. Journal of Open Source Software, 9(93), 5974, https://doi.org/10.21105/joss.05974
We'll add papers that use easyunfold to this list as they come out!
- H. Maleki-Ghaleh et al. Visible Light-Sensitive Sustainable Quantum Dot Crystals of Co/Mg Doped Natural Hydroxyapatite Possessing Antimicrobial Activity and Biocompatibility Small 2024
- K. Eggestad, B. A. D. Williamson, D. Meier and S. M. Selbach Mobile Intrinsic Point Defects for Conductive Neutral Domain Walls in LiNbO3 Journal of Materials Chemistry C 2024
- L. Zhang et al. Study of native point defects in Al0.5Ga0.5N by first principles calculations Computational Materials Science 2024
- Dargahi et al. Synthesis and characterization of zinc-doped hematite nanoparticles for photocatalytic applications and their electronic structure studies by density functional theory Optical Materials 2024
- S. M. Liga & S. R. Kavanagh, A. Walsh, D. O. Scanlon and G. Konstantatos Mixed-Cation Vacancy-Ordered Perovskites (Cs2Ti1–xSnxX6; X = I or Br): Low-Temperature Miscibility, Additivity, and Tunable Stability Journal of Physical Chemistry C 2023
- Y. T. Huang & S. R. Kavanagh et al. Strong absorption and ultrafast localisation in NaBiS2 nanocrystals with slow charge-carrier recombination Nature Communications 2022
- A. T. J. Nicolson et al. Interplay of Static and Dynamic Disorder in the Mixed-Metal Chalcohalide Sn2SbS2I3 Journal of the Americal Chemical Society 2023
- Y. Wang & S. R. Kavanagh et al. Cation disorder engineering yields AgBiS2 nanocrystals with enhanced optical absorption for efficient ultrathin solar cells Nature Photonics 2022 (early version)
At the moment, easyunfold supports VASP and CASTEP, but most of the routines are abstracted from the code specific details. In principle, support for other plane wave DFT code can be added by:
- Implementing a subclass of
WaveFunctionthat handles reading the wave function output. - Implementing functions for reading/writing k-points.
- Adding branches for dispatching based on the
dft_codeattribute of theUnfoldKSetobject in various places within the code.
The Atomic Simulation Environment (ASE) is used by easyunfold for
reading in structures, so structure file IO is natively supported for essentially all public DFT codes.
- Atom-projected band structures are currently only supported for
VASPcalculation outputs. - Gamma-only and non-collinear spin calculations are not supported for
CASTEP.
And those who helped in the development: