pengWann - Descriptors of chemical bonding from Wannier functions

pengwann is a lightweight Python package for calculating descriptors of chemical bonding and local electronic structure from Wannier functions (as obtained from Wannier90).

More specifically, pengwann can be used to calculate the WOHP (Wannier Orbital Hamilton Population) and/or the WOBI (Wannier Orbital Bond index) between a pair (or larger cluster) of atoms. These quantities are analogous to the pCOHP (projected Crystal Orbital Hamilton Population) and pCOBI (projected Crystal Orbital Bond Index) implemented in the LOBSTER code, except that the local basis we choose to represent the Hamiltonian and the density matrix is comprised of Wannier functions rather than pre-defined atomic or pseudo-atomic orbitals. This choice of a Wannier basis has the advantage that (for energetically isolated bands) the spilling factor is strictly 0. For further details as to the advantages and disadvantages of using a Wannier basis, as well as the mathematical formalism behind pengwann in general, please see the Methodology page.

Besides the API reference, a detailed use case of how pengwann can be used to derive WOHPs, WOBIs and the pDOS can be found on the Examples page.

A handful of example outputs from pengwann as applied to rutile. The colour-coded numbers next to the crystal structure are Löwdin-style charges computed for Ti (blue) and O (red).