First-principles calculations of quantum transitions at local centers

Fundamental quantum transitions at local centers are the basis for numerous technologies, including LED, laser, photodetection, and quantum computing. However, accurate theoretical calculations of basic parameters related to these processes remain challenging. In this paper, we review recent developments in first-principles calculations of electronic transitions at local centers in solid-state materials. Specifically, we discuss (1) promising results on hybrid density functional calculations of self-trapped excitons in low-dimensional metal halides and 5d-4f transitions at rare-earth dopants in solids as well as (2) the more challenging case of intra-d-shell transitions at transition-metal ions, which require a higher-level many-body theory to better account for the electron correlation effect. Diffusion quantum Monte Carlo calculations of Mn⁴⁺ emissions in oxides and halides show excellent agreement with experimental results, demonstrating the potentially predictive power in calculating d-d transitions at transition-metal ions and other optical transitions at local centers.