Wannier90 is the most widely-used software for obtaining a Wannier representation of electronic structure calculations, providing a reference implementation--based on maximal localisation in real space of the Wannier functions--that has been widely adopted by the solid state/electronic structure community[1].

Wannier90 is indispensable to a large community of materials scientists working in a range of fundamental and application areas.  Wannier90 provides a well-specified short-ranged real-space representation of the electronic structure of solids, which allows the direct calculation of many materials properties: electric polarisation is naturally the most famous use, along with topological and other properties related to the Berry connection.  This particular real-space representation also allows enormous efficiency improvements in various contexts, by allowing a very fine sampling of the Brillouin zone, which has, for example, revolutionised the calculation of electron-phonon properties.

Wannier90 is broadly used as a starting point in calculation of sophisticated materials properties with a variety of different open-source codes. These include electron-phonon calculations with EPW [2] or perturbo [3], topological properties using WannierTools [4] or Z2Pack [5], Berry phase properties using WannierBerri [6], tight-binding calculations, AiiDA integration, among many others.   Wannier90 provides a framework for post-DFT treatment of electronic correlation, notably in providing a well-defined localised basis for applying dynamical mean-field theory to real materials[7].  Collectively, these efforts constitute an ecosystem of codes based on the output of Wannier90[1] (a registry of such codes is here).

Wannier90 itself effectively abstracts away the more technical issues of electronic structure calculations (basis sets, exchange correlation functional, etc), provides a common framework for different kinds of properties calculations, and is interfaced to the most widely-used electronic structure codes. This means that developments in Wannier90 and Wannier90-related post-processing codes become rapidly available to a very wide community [8] of electronic structure researchers.

The popularity and adoption of Wannier90 has necessitated a transition from an essentially academic software project--originally written by an informal group of academics contributing code developed largely for individual research uses--to a trusted core utility in the materials modelling space.  There is now a user base for Wannier90 that extends very far beyond the developer community.  This success increases the importance of software engineering and code maintenance, necessitating focused effort from the developer community.

Wannier90's importance to so many groups means that the developer community has considerable overlap with other projects in materials modelling.  The proposed developer meeting will bring together technical representatives of many of the large-scale electronic structure codes to provide a special opportunity for community coordination and networking across different physics, chemistry, and materials disciplines.