Muons provide a unique local probe for studying materials at the atomic level, and fluorides have emerged as particularly powerful model systems. In this talk, I will explore how fluorides can be used to track the muon’s quantum information through a sample, opening the door to new insights into how a muon interacts with its environment and enabling rigorous validation of DFT-calculated muon stopping sites. Building on these results, I will show how this approach informs our understanding of more complex magnetic systems, including antiferromagnets and
Coulomb-phase materials. Finally, I will share a brief look at some early work on modelling the excited states of muonium, aimed at gaining new insights into the electronic structure of defects.