Ground and excited states ofKNiF3: Anab initiocluster-model approach

Abstract

Finite cluster models and a variety of ab initio wave functions have been used to study the electronic structure of bulk ${\mathrm{KNiF}}_3$. Several electronic states, including the ground state and some charge-transfer excited states, have been considered. The study of the cluster-model wave functions has permitted an understanding of the nature of the chemical bond in the electronic ground state. This is found to be highly ionic and the different ionic and covalent contributions to the bonding have been identified and quantified. Finally, we have studied the charge-transfer excited states leading to the optical gap and have found that calculated and experimental values are in good agreement. The wave functions corresponding to these excited states have also been analyzed and show that although ${\mathrm{KNiF}}_3$ may be described as a ligand-to-metal charge-transfer insulator there is a strong configuration mixing with the metal-to-metal charge-transfer states.