| 1. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Ab Initio Study of Phase Equilibria in TiCx
- 2002
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Ingår i: Physical Review Letters. - : The American Physical Society. - 0031-9007 .- 1079-7114. ; 88:1, s. 015505-1-01505-4
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Tidskriftsartikel (refereegranskat)abstract
- The phase diagram for the vacancy-ordered structures in the substoichiometric TiCx (x=0.5-1.0) has been established from Monte Carlo simulations with the long-range pair and multisite effective interactions obtained from ab initio calculations. Three ordered superstructures of vacancies (Ti2C, Ti3C2, and Ti6C5) are found to be ground state configurations. Their stability has been verified by full-potential total energy calculations of the fully relaxed structures.
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| 2. |
- Boust, James, et al.
(författare)
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Combining semilocal exchange with dynamical mean-field theory : Electronic structure and optical response of rare-earth sesquioxides
- 2022
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Ingår i: Physical Review B. - 2469-9950. ; 105:8
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Tidskriftsartikel (refereegranskat)abstract
- In rare-earth semiconductors, wide ligand p and rare-earth 5d bands coexist with localized, partially filled 4f shells. A simultaneous description for both extended and localized states represents a significant challenge for first-principles theories. Here, we combine an ab initio dynamical mean-field theory approach to strong local correlations with a perturbative application of the semilocal modified Becke-Johnson exchange potential to correct the semiconducting gap. We apply this method to calculate the electronic structure and optical response of the light rare-earth sesquioxides R2O3 (R=La,Ce,Pr,andNd). Our calculations correctly capture a nontrivial evolution of the optical gap in R2O3 due to a progressive lowering of the 4f states along the series and their multiplet structure. 2p-4f hybridization is found to induce a substantial upward shift for the occupied 4f states occurring within the p-d gap, thus reducing the magnitude of the optical gap. We show that a characteristic plateau observed in the optical conductivity in the Pr and Nd sesquioxides right above their absorption edge is a fingerprint of 4f states located within the p-d gap.
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| 3. |
- Galler, Anna, et al.
(författare)
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Correlated electronic structure and optical response of rare-earth based semiconductors
- 2021
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Ingår i: Physical Review B. - 2469-9950. ; 103:24
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Tidskriftsartikel (refereegranskat)abstract
- The coexistence of Mott localized f states with wide conduction and valence bands in f-electron semiconductors results, quite generically, in a complex optical response with the nature of the absorption edge difficult to resolve both experimentally and theoretically. Here, we combine a dynamical mean-field theory approach to localized 4f shells with an improved description of band gaps by a semilocal exchange-correlation potential to calculate the optical properties of the light rare-earth fluorosulfides LnSF (Ln=Pr, Nd, Sm, Gd) from first principles. In agreement with experiment, we find the absorption edge in SmSF to stem from S-3p to Sm-4f transitions, while the Gd compound behaves as an ordinary p-d gap semiconductor. In the unexplored PrSF and NdSF systems we predict a rather unique occurrence of strongly hybridized 4f-5d states at the bottom of the conduction band. The nature of the absorption edge results in a characteristic anisotropy of the optical conductivity in each system, which may be used as a fingerprint of the relative energetic positions of different states.
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| 4. |
- Galler, Anna, et al.
(författare)
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Intrinsically weak magnetic anisotropy of cerium in potential hard-magnetic intermetallics
- 2021
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Ingår i: npj Quantum Materials. - : Springer Science and Business Media LLC. - 2397-4648. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Cerium-based intermetallics are currently attracting much interest as a possible alternative to existing high-performance magnets containing scarce heavy rare-earth elements. However, the intrinsic magnetic properties of Ce in these systems are poorly understood due to the difficulty of a quantitative description of the Kondo effect, a many-body phenomenon where conduction electrons screen out the Ce-4f moment. Here, we show that the Ce-4f shell in Ce–Fe intermetallics is partially Kondo screened. The Kondo scale is dramatically enhanced by nitrogen interstitials suppressing the Ce-4f contribution to the magnetic anisotropy, in striking contrast to the effect of nitrogenation in isostructural intermetallics containing other rare-earth elements. We determine the full temperature dependence of the Ce-4f single-ion anisotropy and show that even unscreened Ce-4f moments contribute little to the room-temperature intrinsic magnetic hardness. Our study thus establishes fundamental constraints on the potential of cerium-based permanent magnet intermetallics.
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