BinPo: An open-source code to compute the band structure of two-dimensional electron systems

We introduce BinPo, an open-source Python code to compute electronic properties of two-dimensional electron systems. A bulk tight binding Hamiltonian is constructed from relativistic density functional theory calculations represented in the basis of maximally localized Wannier functions. BinPo has a Schrödinger-Poisson solver, integrating an electric field-dependent relative permittivity to obtain self-consistently the confining electrostatic potential energy term in the derived tight binding slab system. The band structure, energy slices, and other properties, along with different projections and orientations can be computed. High resolution and publishable figures of the simulations can be generated. In BinPo, priority has been given to ease-of-use, efficiency, readability and modularity, therefore becoming suitable to produce reliable electronic structures simulations at low computational cost. Along with the code itself, we provide files from first-principles calculations for some materials, instructions of use, and detailed examples of its wide range of capabilities. The code was developed with a focus on the ABO3 perovskite structure-based systems, such as SrTiO3 and KTaO3, because of their increasing impact in the materials community. Some features, such as the projection onto orbital states, are restricted to calculations using the relevant t2g orbitals for this family of materials, yet it is possible to include more elements in the basis for the band structure determination of other systems. The use of a relativistic approach allows for the inspection of the role of spin-orbit coupling and the resulting Rashba effect on the systems. We detail the approaches used in the code, so that it can be further exploited and adapted to other problems, such as adding new materials and functionalities which can strength the initial code scopes.