Ab Initio Calculations on Excited States of Lanthanide Containing Materials

The optical activity derived from the rich manifolds of excited states of lanthanide-containing materials gives them a key role in the development of a large variety of solid-state devices with high societal demand. The intense experimental research in this complex area finds its theoretical grounds mostly in empirical models, but the consideration of ab initio methods as fruitful theoretical tools to handle such a complexity is steadily growing. These methods do not rely on empirical parameters and are based only on the first principles of quantum mechanics. This chapter is dedicated to give a perspective on their use as basic theoretical tools in the area, which must complement and go together with experiments and empirical models.