Theory of defects in non-metallic solids

A general method based upon ab initio quantum mechanical modeling of the region of a solid in the vicinity of a defect or impurity and upon the use of classical modeling of more remote regions in a self-consistent way is being undertaken. The initial progress has been in defining the scope of the model, validation of the several concepts, generation of some necessary theoretical formalism, and finally in an initial study of the excitonic spectra of several alkali iodides. This latter study is significant in several ways. It establishes: the size of cluster needed for such studies; the utility of norm-conserving core replacing pseudo potentials; and the need of treating spin-orbit and multiple structure in a proper way for localized excitation.