Abstract: Colors in several transition metal oxides have often been ascribed to presence of defects/vacancies over the decades.
I will discuss results from our recent work that uses parameter free many body perturbative and exact local approaches
to describe the excitonic absorptions and their spin components that determine the color for these materials and that defects/vacancies were wrongly held responsible for the same. It is in this context that I will discuss the adequacy and sufficiency of a theory in describing multiplet transitions in solid state. Furthering the discussion on multiplets, I will address another outstanding problem of spin, charge and bond disproportionation in rare earth Nickelates. The discussion will be primarily based on a few recently published works and an unpublished one.
Host: Walter Lambrecht