Fig 2 - uploaded by Yakup Emül
Content may be subject to copyright.
Dependence of the ZFSP D on the intrinsic parameters t2 in Eqs. (2)-(4) for (a) Mg vacancy case and (b) Mg-Li substitution case in Cr 3+ doped KMgF 3 .
Source publication
The local structure around Cr3+ centers in perovskite KMgF3 crystal have been investigated through the applications of both an ab-initio, density functional theory (DFT), and a semi empirical, superposition model (SPM), analyses. A supercell approach is used for DFT calculations. All the tetragonal (Cr3+–VMg and Cr3+–Li+), trigonal (Cr3+–VK), and C...
Context in source publication
Context 1
... Figs. 2 and 3 for both Mg Vacancy case and Mg-Li substitution case to see the trends of ZFSP D for all 5 steps followed in SPM calculations. Experimental values are also indicated in the figures as horizontal lines. Fig. 2 shows that the D changes with t 2 linearly for all steps and for both structural cases, while D is almost insensible to b 2 (Fig. 3). It is also clearly seen from both figures that, in accordance with the experimental values, the most probable steps ...
Similar publications
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...
![Loss function in bare nickel at the momentum transfers along (a) [100],...](publication/366655452/figure/fig1/AS:11431281212114638@1702543899774/Loss-function-in-bare-nickel-at-the-momentum-transfers-along-a-100-d-110-and_Q320.jpg)
In this work, we study, in the framework of the ab initio linear-response time-dependent density functional theory, the low-energy collective electronic excitations with characteristic sound-like dispersion, called acoustic plasmons, in bulk ferromagnetic nickel. Since the respective spatial oscillations in slow and fast charge systems involve stat...
Citations
... 7 Previously, we have investigated the local structure around Cr 3þ centers in perovskite KMgF 3 crystal and have shown that ab-initio calculations (DFT), in addition to their various profits on determination of the properties related with quantum chemistry, can be effectively performed to provide the local structural parameters around a paramagnetic dopant ion. 8 resonance (EMR) (EPR and ESR) and ENDOR data, semiempirical calculations (SPM) in general provide the direct information on the local position of the impurity in the lattice structure as well as on its environment involving ligands. So, it was shown that the combination of DFT and SPM calculations is an efficient way to understand the structural mechanisms around a paramagnetic center. ...
... The interaction between the core and valence electrons is handled by Troullier-Martins norm-conserving pseudopotentials 13 in their fully separable form. 14 Based on the advantages and physical reality of the supercell approach over the cluster method 6,15 as previously discussed, 8 we performed our calculations in a 3 Â 3 Â 3 supercell constructed from the conventional KMgF 3 cubic cell for modeling the isolated defect and substitution centers, which have more than 12 Å distance in between in the periodic structure. ...
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 quantitative information has been derived from the DFT calculations on both the electronic structure and the local geometry around Fe3+ centers. All of the trigonal (K-vacancy case, K-Li substitution case, and normal trigonal Fe3+ center case), FeF5O cluster, and tetragonal (Mg-vacancy and Mg-Li substitution cases) centers have been taken into account based on the previously suggested experimental and theoretical inferences. The collaboration between the experimental data and the results of both DFT and SPM calculations provides us to understand most probable structural model for Fe3+ centers in KMgF3.
A detailed microscopic study of the local geometry was performed for the cation sites in fluoroelpasolite Cs2NaYF6 crystal doped with 3d ions (Cr³⁺ and Fe³⁺). Electronic structure of pure, Cr-doped and Fe-doped Cs2NaYF6 has been studied by determining various properties: substitution energies of dopant ions, ionic Mulliken charges, atomic coordinates and unit cell parameters for the optimized structures. Also, the optimized local geometry of all three cation sites before and after the possible dopant ions substitutions has been deduced by DFT calculations. It is shown that the local symmetry of both Y³⁺ and Na⁺ sites maintains its cubic form after both Fe and Cr substitution; however, Fe ions lead quite larger distortion on ligand lengths at Y-site. The optimized structure has been used independently to calculate zero-field splitting parameters (ZFSPs) and crystal field parameters (CFPs) of both Cr³⁺ and Fe³⁺ centers. The calculated ZFSPs of Fe³⁺ ions indicate that the results predicted by SPM for both Y³⁺ site and Na⁺ site agree well with the previous experimental observations of ZFSPs. It can be inferred from the findings regarding both electronic structure and local optimized geometry that substitution of both Cr³⁺ and Fe³⁺ ions for Y³⁺ is more likely in Cs2NaYF6.
Allowing high transition metal (TM) ions doping concentrations makes the fluoroelpasolite crystals Cs2NaMF6 (M = Al, Ga) quite interesting in various laser applications. In this study, we explored the influence of the dopant ions on the electronic and structural properties of Cs2NaAlF6. Particular attention is paid to the influence of trivalent TM ions (Cr³⁺ and Fe³⁺) on the local structure around the possible substitutional cation sites by investigating the optimized geometry around impurity sites due to Cr³⁺ and Fe³⁺ using density functional theory (DFT). The obtained structural data are utilized for the calculations of zero-field splitting (ZFS) parameters (ZFSPs) and crystal field parameters (CFPs) of both dopant ions independently in the frame of semi empirical superposition model (SPM). It is shown that remarkable change on the ZFSPs comes not from the distortion on metal-ligand distance but from that on the angular positions of the ligands around the impurity centers. It is clearly shown that the substitution of both Cr³⁺ and Fe³⁺ ions take place with significant influence on electronic structure and geometry for the trivalent Al³⁺ sites. The presented results here have significant potential to better understand the low-symmetry effects in especially optical applications of Cs2NaAlF6:Cr³⁺ and Cs2NaYF6:Fe³⁺ systems. Particularly, the calculated CFPs for Cs2NaYF6:Fe³⁺ system may serve as the only record in literature.
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.
