lucydot/effmass

========
Features
========

`effmass` can:

**Read in a bandstructure:**
It is assumed you have used a DFT calculator to walk through a 1D slice of the Brillouin Zone, capturing the maxima and minima of interest. `effmass` uses the Python packages [vasppy](https://github.com/bjmorgan/vasppy) for parsing `VASP` output, and `ASE` for parsing the `Castep` output.

**Locate extrema:**
These correspond to the valence band maxima and conduction band minima. Maxima and minima within a certain energy range can also be located.

**Calculate curvature, transport and optical effective masses:**
The curvature (aka inertial) and transport masses are calculated using the derivatives of a fitted polynomial function. The optical effective mass can also be calculated assuming a Kane dispersion.

**Assess the extent of non-parabolicity:**
Parameters of the Kane quasi-linear dispersion are calculated to quantify the extent of non-parabolicity over a given energy range. 

**Calculate the quasi-fermi level for a given carrier concentration:**
Using density-of-states data and assuming no thermal smearing, `effmass` can calculate the energy to which states are occupied. This is a useful approximation to the quasi-Fermi level. *Note: this is only supported for VASP and requires the output file `DOSCAR`.* 

**Plot fits to the dispersion:**
Selected bandstructure segments and approximations to the dispersion (assuming a Kane, quadratic, or higher order fit) can be visualised.

The command line interface provides basic functionality for calculating parabolic effective masses.
For those who have a basic familiarity with Python there is an API which provides access to more (non-parabolic) effective mass definitions. 
Depending on the functionality and level of approximation you are looking for, 
it may be that one of the packages listed [here](https://effmass.readthedocs.io/en/latest/Related%20packages.html) will suit your needs better.

.. figure:: .static/screenshot.png
    :figwidth: 400px
    :alt: "effmass screenshot"