pyscal is a python module for the calculation of local atomic structural environments including Steinhardt’s bond orientational order parameters [1] during post-processing of atomistic simulation data. The core functionality of pyscal is written in C++ with python wrappers using pybind11 which allows for fast calculations and easy extensions in python.

Purpose of Module

Steinhardt’s order parameters are widely used for the identification of crystal structures [3]. They are also used to distinguish if an atom is in a solid or liquid environment [4]. pyscal is inspired by the BondOrderAnalysis code, but has since incorporated many additional features and modifications. The pyscal module includes the following functionalities:

  • calculation of Steinhardt’s order parameters and their averaged version [2].
  • links with the Voro++ code, for the calculation of Steinhardt parameters weighted using the face areas of Voronoi polyhedra [3].
  • classification of atoms as solid or liquid [4].
  • clustering of particles based on a user defined property.
  • methods for calculating radial distribution functions, Voronoi volumes of particles, number of vertices and face area of Voronoi polyhedra, and coordination numbers.

Background Information

See the application documentation for full details.

The utilisation of Dask within the project came about as a result of the E-CAM High Throughput Computing ESDW held in Turin in 2018 and 2019.

Building and Testing


pyscal can be installed directly using Conda by the following statement-

conda install -c pyscal pyscal

pyscal can be built from the repository by-

git clone
cd pyscal
python install --user


pyscal contains automated tests which use the pytest python library, which can be installed by pip install pytest. The tests can be run by executing the command pytest tests/ from the main code directory.


Examples using pyscal can be found here. An interactive notebook using binder is also available.