Ab initio calculations of the excitonic spectra of the alkali iodides including relativistic effects

We extend our previous studies of local excitons in the alkali halides to include relativistic effects such as spin-orbit, mass-velocity, and Darwin corrections. We examine the alkali iodide series and certain features in the optical absorption spectra which are due to local excitons. We find that we must include relativistic effects, as well as an appropriate number of neighboring-ion shells, if we are to compute the excitonic energies accurately.