Diamond as a material of extreme properties has already proved to be a very promising candidate to build nanoengineered devices with a vast variety of applications such as in nanophotonics, optomechanics, photovoltaics and electronics. To harness diamond properties in an optimal way, it is then crucial to understand how its entangled electronic and geometric properties determine the width and the character of the electronic band gap.

To this aim, we conducted a quantum mechanical investigation on diamond-based materials doped with a large variety of doping atoms in different concentrations. Furthermore, we expanded the study by considering cluster defects formed by dopants and carbon vacancies in different geometric configurations; such an expansion allowed us to focus on coupled structural-electronic features even in more detail. We performed extensive electronic and geometric analysis on the ground state geometries, using descriptors such as interatomic distances, orbital polarizations, bond covalencies and Hirshfeld charges. We demonstrate that the specific charge distributions in the ion environment around the dopant govern the width of the band gap; in order to tune the gap, we propose how to choose the suitable dopant atomic types, their concentration, geometric configuration and how to impose convenient axial strains on the structures. Moreover, we discuss different ways of acting on the lattice parameters with the aim of switching the character of the band gap from indirect to direct.

The outcomes of our investigation provide a compact source of information for further use in experimental and technical fields and can lead to the creation of new semiconducting materials. Furthermore, as our investigation protocol is general, the results can be applied to the study of optical and electronic materials of any chemical composition and atomic topology beyond those based on diamond.