Abstract:A simple method for constructing effective Hamiltonians for the 4f(N) and 4f(N - 1)5d energy levels of lanthanide ions in crystals from quantum-chemical calculations is presented. The method is demonstrated by deriving crystal-field and spin-orbit parameters for Ce(3 + ) ions doped in LiYF(4), Cs(2)NaYCl(6), CaF(2), KY(3)F(10) and YAG host crystals from quantum-chemical calculations based on the DV-Xα method. Good agreement between calculated and fitted values of the crystal-field parameters is obtained. The m… Show more
“…Crystal field—calculated by OCP method for Ce 3+ —splits the eight-fold degenerate 2 F 7/2 state into states with energies 0.25, 0.32, 0.46 eV. These results are comparable with experimental and theoretical CF splittings of Ce 3+ doped in CaF 2 34 – 36 and YAG (Y 3 Al 5 O 12 ) 34 , 37 hosts. Fig.…”
Previous studies have shown that a large solid-state entropy of reduction increases the thermodynamic efficiency of metal oxides, such as ceria, for two-step thermochemical water splitting cycles. In this context, the configurational entropy arising from oxygen off-stoichiometry in the oxide, has been the focus of most previous work. Here we report a different source of entropy, the onsite electronic configurational entropy, arising from coupling between orbital and spin angular momenta in lanthanide f orbitals. We find that onsite electronic configurational entropy is sizable in all lanthanides, and reaches a maximum value of ≈4.7 k
B per oxygen vacancy for Ce4+/Ce3+ reduction. This unique and large positive entropy source in ceria explains its excellent performance for high-temperature catalytic redox reactions such as water splitting. Our calculations also show that terbium dioxide has a high electronic entropy and thus could also be a potential candidate for solar thermochemical reactions.
“…Crystal field—calculated by OCP method for Ce 3+ —splits the eight-fold degenerate 2 F 7/2 state into states with energies 0.25, 0.32, 0.46 eV. These results are comparable with experimental and theoretical CF splittings of Ce 3+ doped in CaF 2 34 – 36 and YAG (Y 3 Al 5 O 12 ) 34 , 37 hosts. Fig.…”
Previous studies have shown that a large solid-state entropy of reduction increases the thermodynamic efficiency of metal oxides, such as ceria, for two-step thermochemical water splitting cycles. In this context, the configurational entropy arising from oxygen off-stoichiometry in the oxide, has been the focus of most previous work. Here we report a different source of entropy, the onsite electronic configurational entropy, arising from coupling between orbital and spin angular momenta in lanthanide f orbitals. We find that onsite electronic configurational entropy is sizable in all lanthanides, and reaches a maximum value of ≈4.7 k
B per oxygen vacancy for Ce4+/Ce3+ reduction. This unique and large positive entropy source in ceria explains its excellent performance for high-temperature catalytic redox reactions such as water splitting. Our calculations also show that terbium dioxide has a high electronic entropy and thus could also be a potential candidate for solar thermochemical reactions.
“…Nevertheless, it is noteworthy to highlight the considerable efforts in this context made by the theoreticians [10][11][12][13][14][15] inasmuch as the possibility to make a comparison between different approaches to the problem is now established. [16][17][18] Amongst various theoretical approaches to the problem, from empirical fit of experimental data to phenomenological Hamiltonian 14,15 to ab initio methodologies, 10,13 Density Functional Theory (DFT) offers a better compromise, given the acknowledged advantages of this frame in many applications. Moreover the particular procedure of controlling the spin and the orbital occupation schemes in DFT simplifies the computation and enables DFT to be the method of choice adapted to this particular problem.…”
We deal with the computational determination of the electronic structure and properties of lanthanide ions in complexes and extended structures having open-shell f and d configurations. Particularly, we present conceptual and methodological issues based on Density Functional Theory (DFT) enabling the reliable calculation and description of the f -d transitions in lanthanide doped phosphors. We consider here the optical properties of the Pr 3+ ion embedded into various solid state fluoride host lattices, for the prospection and understanding of the so-called quantum cutting process, being important in the further quest of warm-white light source in light emitting diodes (LED). We use the conceptual formulation of the revisited ligand field (LF) theory, fully compatibilized with the quantum chemistry tools: LFDFT. We present methodological advances for the calculations of the Slater-Condon parameters, the ligand field interaction and the spin-orbit coupling constants, important in the non-empirical parameterization of the effective Hamiltonian adjusted from the ligand field theory. The model shows simple procedure using less sophisticated computational tools, which is intended to contribute to the design of modern phosphors and to help to complement the understanding of the 4f n -4f nÀ1 5d 1 transitions in any lanthanide system.
“…In the second, more recent, approach the 4f states are represented by Wannier functions, 28,29,31 while the charge density and, correspondingly, the Kohn-Sham potential are generated by self-consistent DFT calculations with 4f states treated as semi-core. An additional ad hoc parameter is used to correct the charge transfer energy between 4f and conduction bands.…”
We apply the first-principles density functional theory + dynamical mean field theory framework to evaluate the crystal-field splitting on rare-earth sites in hard magnetic intermetallics. An atomic (Hubbard-I) approximation is employed for local correlations on the rare-earth 4f shell and selfconsistency in the charge density is implemented. We reduce the density functional theory selfinteraction contribution to the crystal-field splitting by properly averaging the 4f charge density before recalculating the one-electron Kohn-Sham potential. Our approach is shown to reproduce the experimental crystal-field splitting in the prototypical rare-earth hard magnet SmCo5. Applying it to RFe12 and RFe12X hard magnets (R =Nd, Sm and X =N, Li), we obtain in particular a large positive value of the crystal-field parameter A 0 2 r 2 in NdFe12N resulting in a strong out-of-plane anisotropy observed experimentally. The sign of A 0 2 r 2 is predicted to be reversed by substituting N with Li, leading to a strong out-of-plane anisotropy in SmFe12Li. We discuss the origin of this strong impact of N and Li interstitials on the crystal-field splitting on rare-earth sites.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
