FIG 3 - uploaded by Muhammed Acikgoz
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Optimized structure around Fe 3þ ion in KMgF 3 crystal for (a) the Mg vacancy case and (b) the Mg-Li substitution case (from Step-VI). The directional movements (scaled blue arrows) of the atoms with respect to the structure in case-0 are shown.
Source publication
Analyses of the local crystal and electronic structure in the vicinity of Fe3+ centers in perovskite KMgF3 crystal have been carried out in a comprehensive manner. A combination of density functional theory
(DFT) and a semi-empirical superposition model (SPM) is used for a complete analysis of all Fe3+ centers in this study for the first time. Some...
Context in source publication
Context 1
... is clear that the change in K vacancy case is more significant than that in K-Li substitution case, especially the total charge of Fe. The total charge values of FeF 5 O center case (see Table III and Figure 3) are given in column-C. The quite small changes are seen in charges of all Fe 3þ ion, F ax , and F eq ligands. ...
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Citations
... High-pressure structural, elastic and electronic properties of the scintillator host material KMgF 3 were obtained in [14]. Investigation of the Fe 3+ centers in perovskite KMgF 3 through a combination of ab initio (density functional theory) and semiempirical (superposition model) calculations have been presented in work [15]. ...
First-principles calculations have been carried out to study the electronic properties of the KMgF3 perovskite crystal. On first stage the calculations were performed within the generalized gradient approximation. On the second stage we have evaluated the quasiparticle corrections to the generalized gradient approximation band structure. These significantly improved electronic energies have been found here for the first time on base of the quasiparticle approach as implemented in the ABINIT code. Also, the pressure dependent parameters of electronic energy band spectra were found in the generalized gradient approximation. For the first time the pressure dependent electronic band energies have been evaluated within the quasiparticle approach. The generalized gradient approximation band gap parameters are in good agreement with the literature data, obtained with local density approximation or generalized gradient approximation exchange-correlation functionals and are much underestimated compared with the experiment. The quasiparticle band gap agrees well with the measured value.
We review applications of the superposition model (SPM) in EMR area, which enables semi-empirical modeling of zero-field splitting (ZFS) parameters (ZFSPs) for transition ions in crystals by separation of geometrical and physical information. Nomenclature used for ZFS and crystal field (CF) Hamiltonians is presented to expose common framework underlying two independent implementations: SPM/ZFS and SPM/CF, which require distinct model parameters. SPM/ZFSP applications in EMR area for S-state 3d⁵ (4f⁷) ions and 3dN ions with orbital singlet ground state are reviewed. SPM/ZFS methodology for MLn complexes [central metal (M) ion surrounded by n ligands (L)] with specific symmetry is presented. SPM-related computer packages combined with other methods, role of axis systems in SPM analysis, and structural models for several ion-host systems, are discussed. Extensive survey of SPM/ZFS applications is provided to elucidate usefulness of SPM modeling for interpretation of ZFSPs. This review is geared for EMR practitioners interested in practical utilization of SPM/ZFS (or SPM/CFP) analysis. Database of SPM/ZFS references is compiled for studies of single molecule magnets and single ion magnets based on transition ions. Due to its comprehensiveness, suitable sets of model parameters required for practical utilization SPM/ZFS may be easily located using source references as pointers.
The structural properties of 3d ions (Cr³⁺ and Fe³⁺) centers in Cs2NaGaF6 have been investigated by performing density functional theory (DFT) and semi-empirical superposition model (SPM) calculations. The local geometry (i.e. equilibrium ligand distance and angles between the host cation ion (Cs⁺, Na⁺, or Ga³⁺) and F ligands) for pure, Cr³⁺ doped and Fe³⁺ doped structures have been determined after a fully relaxed geometry optimization at each lattice site. The previous experimental zero-field splitting (ZFS) parameters (ZFSPs) have been analyzed by SPM calculations using the obtained structural properties from DFT. The combination of two methods provide us to confirm the main result of the previous electron magnetic resonance and optical investigations stating that transition metal (TM) ions substitute for octahedral sites instead of being distributed randomly in the lattice of Cs2NaGaF6.
