Extracting Excited States Energies from a Density Functional Database.

The development of new computational tools is greatly helped by testing any new method on small and well-known systems, such as rare earth atoms, whose properties are well established through experiments and calculations, such as density functional theory (DFT). Such calculations can run fairly faster than those of molecules or clusters. Here we present a method for approaching configuration interaction accuracy by analyzing all the non self consistent data that is encountered during the path to self consistency. Our results have employed density functional approximations but our method can use data from any and all single determinantal data base(s). Applications of our method to core and valence level excitations of rare earth atoms are presented.