Modeling of Defects in Silver Halides

Abstract

Modeling methods are now established as a major technique in defect physics and chemistry. Indeed, much of the contemporary understanding of complex defect processes derives from applying these techniques in conjunction with experimental methods.The silver halides possess unusual defect properties and pose unique challenges to simulation studies. This article aims to outline the general features of defect simulations, and to review the status of their application to the defect properties of silver halides.Technical aspects of the field have been detailed elsewhere, so this account is brief. An important feature of recent studies of the silver halides concerns developments in interatomic potentials, which will be considered, followed by a presentation and discussion of the calculated defect parameters.The basis of the simulation techniques is the specification of an interatomic potential model for the system, i.e., an analytical or possibly a numerical description of the energy of the system as a function of atomic coordinates. For polar materials, the model must include the following terms: Coulomb and short-range energies, and ionic polarization.To evaluate these terms, charges must be assigned to all atoms. In most studies reported to date, the fully ionic model has been used, i.e., integral charges have been assigned. The procedure has been followed in modeling the silver halides. Care must be taken in summing r-1 terms. Simple truncation procedures give unreliable results.