Character of the electronic ground state and of charge‐transfer excited states in ionic solids: An ab initio cluster model approach

Abstract

The electronic structure of the ground electronic state and of some special charge-transfer excited states in ionic solids is examined from the ab initio cluster model approach. Different ab initio wave functions, including a frozen orbital approach, the Hartree-Fock self-consistent field, and multireference configuration interaction wave functions, are considered and analyzed using different theoretical techniques. We explicitly consider some alkaline-earth oxides such as CaO, a more difficult case such as Al2O3, a transitionmetal oxide such as NiO, and a system with a more complicated structure such as KNiF3. Analysis of ab initio wave functions in terms of valence bond components shows that all these compounds are largely ionic, thus supporting the simple picture arising from the ionic model. However, the nature of the excited states is more complex. Alkaline-earth oxides lowest excited states are essentially described as charge-transfer excitations dominated by a single resonant valence bond structure and the calculated energy difference is comparable to the experimental optical gap. In the case of Al2O3, the electronic spectra presents excitonic features and the local charge-transfer excitation excited states provide a reasonable representation of these phenomena. Finally, several different valence bond structures are present in the lowest electronic states of KNiF3.

Role of charge transfer configurations in LaMnO3, CaMnO3, and CaFeO3

“…Finally, we compare our results to those obtained by Casanovas et al, 28 who estimated the covalent contributions to the wave function for NiO based on similar considerations as in this work. They performed large CI calculations using a set of nonoptimized atomic orbitals.…”

Ab Initio Modeling of the Metal−Support Interface: The Interaction of Ni, Pd, and Pt on MgO(100)

“…Since MgO is a largely ionic system, − it is necessary to include the long-range Madelung potential. In fact, recent work has shown that while the Madelung potential develops quite rapidly even for moderately large clusters, considerable errors can arise from models that do not explicitly account for the Madelung field .…”

Single-Crystal 27Al NMR of Andalusite and Calculated Electric Field Gradients: the First Complete NMR Assignment for a 5-Coordinate Aluminum Site

“…These two methods have been applied to a variety of Al-containing systems. Corundum, α-Al 2 O 3 , has been a test of calculations for systems with an infinite covalent network − and the subject of the first complete measurement of the 27 Al chemical shift anisotropy − In related work, the 25 Mg and 17 O EFGs in the mineral forsterite, Mg 2 SiO, were calculated with impressive accuracy with DFT methods …”

“…These two methods have been applied to a variety of Al-containing systems. Corundum, R-Al 2 O 3 , has been a test of calculations for systems with an infinite covalent network [61][62][63][64][65][66][67] and the subject of the first complete measurement of the 27 Al chemical shift anisotropy. 68 Small clusters have been studied as models for aluminosilicates and zeolites.…”