Semiconductor heterostructures represent key ingredients for application in novel light emitters and detectors, energy harvesting, or quantum technology. Numerical simulations of the optoelectronic properties of heterostructures such as thin films, nanowires, and quantum dots facilitate both a detailed and systematic understanding of observations from experiment as well as theory-guided design of nanostructures such that they fulfill the requirements of a specific application. We will provide an overview of our modelling capabilities of the electronic properties of semiconductor heterostructures using continuum-based multiband k.p models, implemented within the plane-wave framework of the SPHInX library [1,2]. We illustrate the applicability of our approach by showcasing some recent example studies [3]. 1: sxrepo.mpie.de 2: S. Boeck et al., Computer Phys. Commun. 182, 543 (2011) 3: O. Marquardt, Comp. Mat. Sci. 194, 110318 (2021)