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📖 Official Documentation 📖

🙋 Support Forum 🙋

📝 JOSS Paper 📝

IFermi is a Python (3.9+) library and set of command-line tools for the generation, analysis, and visualisation of Fermi surfaces and Fermi slices. The goal of the library is to provide fully featured FermiSurface and FermiSlice objects that allow for easy manipulation and analysis. The main features include:

• Interpolation of electronic band structures onto dense k-point meshes.
• Extraction of Fermi surfaces and Fermi slices from electronic band structures.
• Projection of arbitrary properties onto Fermi surfaces and Fermi slices.
• Tools to calculate Fermi surface dimensionality, orientation, and averaged projections, including Fermi velocities.
• Interactive visualisation of Fermi surfaces and slices, with support for mayavi, plotly and matplotlib.
• Generation and visualisation of spin-texture.

IFermi's command-line tools only work with VASP calculations but support for additional DFT packages will be added in the future.

Quick start

The online documentation provides a full description of the available command-line options.

Analysis

Fermi surface properties, including dimensionality and orientation can be extracted from a vasprun.xml file using:

bash ifermi info --property velocity

```

Fermi Surface Summary

# surfaces: 5 Area: 32.75 Å⁻² Avg velocity: 9.131e+05 m/s

Isosurfaces ~~~~~~~~~~~

  Band    Area [Å⁻²]    Velocity avg [m/s]   Dimensionality    Orientation
------  ------------  --------------------  ----------------  -------------
     6         1.944             7.178e+05         2D           (0, 0, 1)
     7         4.370             9.092e+05      quasi-2D        (0, 0, 1)
     7         2.961             5.880e+05         2D           (0, 0, 1)
     8         3.549             1.105e+06      quasi-2D        (0, 0, 1)
     8         3.549             1.105e+06      quasi-2D        (0, 0, 1)

```

Visualisation

Three-dimensional Fermi surfaces can be visualized from a vasprun.xml file using:

bash ifermi plot

The two-dimensional slice of a Fermi surface along the plane specified by the miller indices (j k l) and distance d can be plotted from a vasprun.xml file using:

bash ifermi plot --slice j k l d

Python library

The ifermi command line tools are build on the IFermi Python library. Here is an example of how to load DFT calculation outputs, interpolate the energies onto a dense mesh, generate a Fermi surface, calculate Fermi surface properties, and visualise the surface. A more complete summary of the API is given in the API introduction page and in the API Reference page in the documentation.

```python from pymatgen.io.vasp.outputs import Vasprun from ifermi.surface import FermiSurface from ifermi.interpolate import FourierInterpolator from ifermi.plot import FermiSlicePlotter, FermiSurfacePlotter, saveplot, showplot from ifermi.kpoints import kpointsfrombandstructure

load VASP calculation outputs

vr = Vasprun("vasprun.xml") bs = vr.getbandstructure()

interpolate the energies onto a dense k-point mesh

interpolator = FourierInterpolator(bs) densebs, velocities = interpolator.interpolatebands(return_velocities=True)

generate the Fermi surface and calculate the dimensionality

fs = FermiSurface.frombandstructure( densebs, mu=0.0, wignerseitz=True, calculate_dimensionality=True )

generate the Fermi surface and calculate the group velocity at the

center of each triangular face

densekpoints = kpointsfrombandstructure(densebs) fs = FermiSurface.frombandstructure( densebs, mu=0.0, wignerseitz=True, calculatedimensionality=True, propertydata=velocities, propertykpoints=densekpoints )

number of isosurfaces in the Fermi surface

fs.n_surfaces

number of isosurfaces for each Spin channel

fs.nsurfacesper_spin

the total area of the Fermi surface

fs.area

the area of each isosurface

fs.area_surfaces

loop over all isosurfaces and check their properties

the isosurfaces are given as a list for each spin channel

for spin, isosurfaces in fs.isosurfaces.items(): for isosurface in isosurfaces: # the dimensionality (does the surface cross periodic boundaries) isosurface.dimensionality

    # what is the orientation
    isosurface.orientation

    # does the surface have face properties
    isosurface.has_properties

    # calculate the norms of the properties
    isosurface.properties_norms

    # calculate scalar projection of properties on to [0 0 1] vector
    isosurface.scalar_projection((0, 0, 1))

    # uniformly sample the surface faces to a consistent density
    isosurface.sample_uniform(0.1)

plot the Fermi surface

fsplotter = FermiSurfacePlotter(fs) plot = fsplotter.get_plot()

generate Fermi slice along the (0 0 1) plane going through the Γ-point.

fermislice = fs.getfermi_slice((0, 0, 1))

number of isolines in the slice

fermislice.nlines

do the lines have segment properties

fermislice.hasproperties

plot slice

sliceplotter = FermiSlicePlotter(fermislice) plot = sliceplotter.getplot()

saveplot(plot, "fermi-slice.png") # saves the plot to a file showplot(plot) # displays an interactive plot ```

Citing IFermi

If you find IFermi useful, please encourage its development by citing the following paper in your research output:

Ganose, A. M., Searle, A., Jain, A., Griffin, S. M., IFermi: A python library for Fermi surface generation and analysis. Journal of Open Source Software, 2021, 6 (59), 3089

Installation

The recommended way to install IFermi is in a conda environment.

bash conda create --name ifermi pip cmake numpy conda activate ifermi conda install -c conda-forge pymatgen boltztrap2 pyfftw pip install ifermi `

IFermi is currently compatible with Python 3.9+ and relies on a number of open-source python packages, specifically:

• pymatgen for parsing DFT calculation outputs.
• BoltzTrap2 for band structure interpolation.
• trimesh for manipulating isosurfaces.
• matplotlib, mayavi, and plotly for three-dimensional plotting.

Running tests

The integration tests can be run to ensure IFermi has been installed correctly. First download the IFermi source and install the test requirements.

git clone https://github.com/fermisurfaces/IFermi.git cd IFermi pip install .[tests]

The tests can be run in the IFermi folder using:

bash pytest

Need Help?

Ask questions about the IFermi Python API and command-line tools on the IFermi support forum. If you've found an issue with IFermi, please submit a bug report here.

What’s new?

Track changes to IFermi through the changelog.

Contributing

We greatly appreciate any contributions in the form of a pull request. Additional information on contributing to IFermi can be found here. We maintain a list of all contributors here.

License

IFermi is made available under the MIT License (see LICENSE file).

Acknowledgements

Developed by Amy Searle and Alex Ganose. Sinéad Griffin designed and led the project.