| 1. |
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| 2. |
- Katcko, K., et al.
(författare)
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Spin-driven electrical power generation at room temperature
- 2019
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Ingår i: Communications Physics. - : NATURE PUBLISHING GROUP. - 2399-3650. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- On-going research is exploring novel energy concepts ranging from classical to quantum thermodynamics. Ferromagnets carry substantial built-in energy due to ordered electron spins. Here, we propose to generate electrical power at room temperature by utilizing this magnetic energy to harvest thermal fluctuations on paramagnetic centers using spintronics. Our spin engine rectifies current fluctuations across the paramagnetic centers' spin states by utilizing so-called 'spinterfaces' with high spin polarization. Analytical and ab-initio theories suggest that experimental data at room temperature from a single MgO magnetic tunnel junction (MTJ) be linked to this spin engine. Device downscaling, other spintronic solutions to select a transport spin channel, and dual oxide/organic materials tracks to introduce paramagnetic centers into the tunnel barrier, widen opportunities for routine device reproduction. At present MgO MTJ densities in next-generation memories, this spin engine could lead to 'always-on' areal power densities that are highly competitive relative to other energy harvesting strategies.
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| 3. |
- Galanakis, I, et al.
(författare)
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Sign reversal of the orbital moment via ligand states - art. no. 172405
- 2001
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Ingår i: PHYSICAL REVIEW B. - : AMERICAN PHYSICAL SOC. - 0163-1829. ; 6317:17, s. 2405-
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Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that the coupling between spin and orbital moments in magnetic systems may-for certain materials-be reversed from antiparallel to parallel, via the influence of ligand states. This is exemplified by first-principles calculations for an
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| 4. |
- Galanakis, I, et al.
(författare)
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Tuning the orbital moment in transition metal compounds using ligand states
- 2001
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Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. - : IOP PUBLISHING LTD. - 0953-8984. ; 13:20, s. 4553-4566
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Tidskriftsartikel (refereegranskat)abstract
- The influence of ligand states on the orbital magnetism of a 3d atom in a ferromagnetic compound has been studied using an ab initio technique. It is shown, using VAu4, MnAu4 and VPt3 as examples, that the large spin-orbit coupling of the 5d atom is respo
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| 5. |
- Wills, J. M., et al.
(författare)
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Total Energy and Forces : Some Numerical Examples
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 101-109
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Bokkapitel (refereegranskat)abstract
- Numerical examples of calculations of total energy, equation of state and Hellman-Feynman forces are given. The calculation of first principles phonons is also exemplified with fcc Al and bcc U. A comparison between a few selected exchange and correlation functionals is also made for the calculation of the equation of state.
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| 6. |
- Ahuja, R, et al.
(författare)
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Optical properties of graphite from first-principles calculations
- 1997
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Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - : AMER INST PHYSICS. - 0163-1829. ; 55:8, s. 4999-5005
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present theoretical results for the frequency-dependent dielectric response, both for the electric field parallel and perpendicular to the c axis of graphite. The calculations are performed using a full-potential linear muffin-tin orbital method. Our c
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| 7. |
- Araujo, Carlos Moyses, et al.
(författare)
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Electronic and optical properties of MgH2: a first-principle GW investigation
- 2005
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 98:9, s. 096106-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of MgH2 is studied using the state of the art all-electron projector-augmented-wave GW approximation. Both the ground-state and the high-pressure transformations are considered in this investigation. We have found an indirect (direct) band-gap of 5.58 eV (6.52 eV) for α-MgH2, which has a good agreement with the experimental findings. For the γ- and β-phases, we have found indirect (direct) band-gap values of 5.24 eV (5.33 eV) and 3.90 eV (4.72 eV), respectively. The optical properties are investigated by means of the complex dielectric function, which is calculated within the framework of a full-potential linearized augmented plane wave method and corrected by scissor operators. All phases are found to be color neutral insulators.
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| 8. |
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| 9. |
- Iusan, Diana, et al.
(författare)
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Effect of diffusion and alloying on the magnetic and transport properties of Fe/V/Fe trilayers
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:2, s. 024412-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic and transport properties of the Fe/V/Fe(001) trilayers were studied using the self-consistent Green's function technique based on the tight-binding linear muffin-tin orbital method in the atomic-sphere approximation. The coherent potential approximation was used to describe the effects of interdiffusion and alloying at the interfaces on the properties of the semi-infinite bcc Fe(001)/mFe/nV/mFe/Fe(001) trilayers. The electric conductance was calculated using the Kubo-Landauer formalism, in the current-perpendicular-to-plane geometry. It is shown that a dipole moment is created at the Fe/V interface due to the charge transfer from vanadium to iron, and a small induced magnetic moment is present in the first vanadium layer and is antiparallel to that of iron. The interlayer exchange coupling shows rapid oscillations for small spacer thicknesses, and the interdiffusion and alloying at the interface stabilize the ferromagnetic coupling. Moreover, the interdiffusion reduces the vanadium-induced magnetic moment and increases the iron magnetic moment at the interface. The giant magnetoresistance (GMR) ratio presents damped oscillations as a function of the vanadium spacer thickness. The interdiffusion and the presence of Mn impurities at the interface reduce considerably the GMR ratio and produce results that are in agreement with experimental data.
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| 10. |
- Kanchana, V., et al.
(författare)
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Electronic structure and x-ray magnetic circular dichroism of Sr2FeMoO6 : Ab initio calculations
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:22
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical investigations of the electronic structure, x-ray absorption, and x-ray magnetic circular dichroism (XMCD) at the Fe L-2,L-3 and Mo L-2,L-3 edges of Sr2FeMoO6 are carried out by means of the generalized gradient approximation. The magnetic coupling between Fe and Mo is found to be antiparallel, which gives direct confirmation of ferrimagnetic ordering and settles controversies existing between the earlier experimental reports. This is also confirmed by our good agreement of the Mo L-2,L-3 edges with experiment. Using our theoretical spectra, we recalculate the spin and orbital magnetic moments by means of the XMCD sum rules and compare the results with a direct self-consistent calculation and experiment.
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| 11. |
- Kim, D. Y., et al.
(författare)
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Crystal structure of the pressure-induced metallic phase of SiH4 from ab initio theory
- 2008
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 105:43, s. 16454-16459
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Tidskriftsartikel (refereegranskat)abstract
- Metallization of pure solid hydrogen is of great interest, not least because it could lead to high-temperature superconductivity, but it continues to be an elusive goal because of great experimental challenges. Hydrogen-rich materials, in particular, CH4, SiH4, and GeH4, provide an opportunity to study related phenomena at experimentally achievable pressures, and they too are expected to be high-temperature superconductors. Recently, the emergence of a metallic phase has been observed in silane for pressures just above 60 GPa. However, some uncertainty exists about the crystal structure of the discovered metallic phase. Here, we show by way of elimination, that a single structure that possesses all of the required characteristics of the experimentally observed metallic phase of silane from a pool of plausible candidates can be identified. Our density functional theory and GW calculations show that a structure with space group P4/nbm is metallic at pressures > 60 GPa. Based on phonon calculations, we furthermore demonstrate that the P4/nbm structure is dynamically stable at > 43 GPa and becomes the ground state at 97 GPa when zero-point energy contributions are considered. These findings could lead the way for further theoretical analysis of metallic phases of hydrogen-rich materials and stimulate experimental studies.
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| 12. |
- Kim, Duck Young, et al.
(författare)
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Structurally induced insulator-metal transition in solid oxygen : A quasiparticle investigation
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77:9, s. 092104-
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Tidskriftsartikel (refereegranskat)abstract
- Structural phase transition of solid oxygen has been investigated by using ab initio calculations based on density functional theory. We found sudden jumps in structural parameters at the transition pressure, which confirm that the epsilon (epsilon) phase undergoes a first-order isostructural phase transformation to the zeta (zeta) phase. In particular, this happens without any molecular dissociation. Using the GW approximation to calculate the band-gap closure under high pressure, we show that the structural transition is accompanied by an insulator-metal transition, contrary to a standard density functional calculation which predicts a metallization at a much lower pressure in the epsilon phase.
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| 13. |
- Lebègue, Sébastien, et al.
(författare)
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Molecular dynamics simulation and chemical bonding analysis of MgB2C2
- 2006
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 37:3, s. 220-225
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Tidskriftsartikel (refereegranskat)abstract
- The possible superconducting material MgB2C2 is studied by means of the Projector Augmented Plane wave method. The experimental lattice parameters and internal coordinates are reproduced with accuracy by means of a molecular dynamics calculation. A chemical bonding analysis is performed and it is found that the charge transfer from the Mg atoms to the BC network is not complete, meaning that a significant part of covalent bonding is present in this bond. In addition, a crystal orbital overlap population calculation reveals the degree of covalent bonding between atoms. This analysis is of particular importance and helps improve our general understanding of the superconductivity in these type of materials.
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| 14. |
- Lebègue, Sébastien, et al.
(författare)
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Quasiparticle and optical properties of BeH2
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:3, s. 036223-
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Tidskriftsartikel (refereegranskat)abstract
- The quasiparticle and optical properties of BeH2 are computed by means of the all-electron GW approximation in conjunction with the projector augmented wave (PAW) method. The GW approximation, through the calculation of the self-energy and the optical dielectric function in the random phase approximation, shows that BeH2 is a large band gap insulator. The results are discussed in view of future experiments.
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| 15. |
- Scheicher, Ralph H., et al.
(författare)
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Cubic metallic phase of aluminum hydride showing improved hydrogen desorption
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:20
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Tidskriftsartikel (refereegranskat)abstract
- We report on our results calculated from density functional theory and GW of the dehydrogenation properties in a cubic phase of AlH3. The metallic nature of the electronic structure entails a more favorable hydrogen removal energy which is lowered by 75% compared to the insulating hexagonal phase. This remarkable reduction in the Al-H bond strength bears important consequences for feasible applications of AlH3 as an on-board hydrogen storage material for mobile applications. We suggest that the cubic phase could be prepared and stabilized experimentally at ambient pressure by off-board quenching.
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| 16. |
- Sorgenfrei, Felix, et al.
(författare)
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Theory of x-ray absorption spectroscopy for ferrites
- 2024
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:11
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Tidskriftsartikel (refereegranskat)abstract
- The theoretical calculation of the interaction of electromagnetic radiation with matter remains a challenging problem for contemporary ab initio electronic structure methods, in particular, for x-ray spectroscopies. This is not only due to the strong interaction between the core hole and the photoexcited electron, but also due to the elusive multiplet effects that arise from the Coulomb interaction among the valence electrons. In this work we report a method based on density functional theory in conjunction with multiplet ligand-field theory to investigate various core-level spectroscopies, in particular, x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The developed computational scheme is applied to the L 2 , 3 XAS and XMCD edges of magnetite (Fe 3 O 4 ) as well as cobalt ferrite (CoFe 2 O 4 ) and nickel ferrite (NiFe 2 O 4 ). The results are in overall good agreement with experimental observations, both regarding the XAS L 2 / L 3 branching ratio, the peak positions, as well as the relative intensities. The agreement between theory and experiment is equally good for XAS and the XMCD spectra, for all studied systems. The results are analyzed in terms of e g and t 2 g orbital contribution, and the robustness of the spectra with regard to the uncertainties of the Slater parameters is investigated. The analysis also highlights the strong effect of the 2 p -3 d interaction in x-ray spectroscopy.
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| 17. |
- Vaitheeswaran, G., et al.
(författare)
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Ab initio calculated X-ray magnetic circular dichroism of Sr2CrReO6
- 2008
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 84:4
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio calculated X-ray absorption and X-ray magnetic circular dichroism (XMCD) spectra at the Cr and Re L-2,L-3 edges for the double perovskite Sr2CrReO6 are compared with experiment. The main features of the experimental spectra are reproduced by the calculations, however, the amplitudes of several structures are significantly over- or underestimated. The calculated spin and orbital magnetic moments for Cr and Re agree with those obtained by means of XMCD sum rules, except for the Cr orbital moment, illustrating that numerical uncertainties can be large for small moments. It is also argued that the Re moments are induced and not intrinsic.
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| 18. |
- Wills, John M., et al.
(författare)
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A Database of Electronic Structures
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 179-181
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this short chapter, an data-base of electronic structures are described and a method in data-mining technology is presented, for how such a data-basemight be used to search for new functional materials.
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| 19. |
- Wills, John M., et al.
(författare)
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Chemical Bonding of Solids
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 111-131
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this chapter an analysis of chemical binding of materials is made, introducing concepts like the crystal orbital overlap population. Numerical examples of equilibrium volume of the transition metals, lanthanides and actinides are presented. Calculated equilibrium volumes of refractory materials are compared to experimental values. The cohesive energy is defined, and calculations are compared to experiment for the lanthanides. The structural stability of sp-bonded metals, transition metals, and actinides is discussed. In addition calculations of mixed valent materials, using the Kimbal–Falicov model are described. The chapter ends with a description of calculations of elastic constants of materials. For all calculations a comment on convergence of different computational parameters is made.
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| 20. |
- Wills, John M., et al.
(författare)
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Consequences of Infinite Crystals and Symmetries
- 2010
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Ingår i: Springer Series in Solid-State Sciences. - Berlin, Heidelberg : Springer Nature. ; , s. 21-24
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this short chapter the consequences of periodicity and general symmetry of a crystal is presented. The seven crystal lattices are introduced and as an example the point group operations of a cubic material are illustrated.
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| 21. |
- Wills, John M., et al.
(författare)
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Density Functional Theory and the Kohn–Sham Equation
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 7-19
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The basic formulas of density functional theory (DFT) are derived, together with a discussion about the form and accuracy of different approximations to the energy functional used in DFT. Central concepts in DFT, like exchange and correlation hole, exchange and correlation energy, and the Kohn–Sham equation are presented. A short description about the historical development of density functional theory as also given.
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| 22. |
- Wills, John M., et al.
(författare)
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Dynamical Mean Field Theory
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 75-87
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The basic reasons for why the common approximation to the exchange and correlation energy of density functional theory is inaccurate for certain materials are outlined. A possible fix to this problem, in terms of dynamical mean field theory (DMFT) is described, and details of how it is implemented in the FP-LMTO method are presented. The different choices of correlated orbitals which are to be considered in DMFT are also given. Examples of DMFT calculations are presented using different approximations to the ‘impurity part’ of the DMFT calculations.
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| 23. |
- Wills, John M., et al.
(författare)
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Excitated State Properties
- 2010
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Ingår i: Springer Series in Solid-State Sciences. - Berlin, Heidelberg : Springer Nature. ; , s. 145-178
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The phenomenological theory of optical properties of materials is presented.The general theory of calculations of optical properties from first principlestheory is given, with special emphasis on the implementation in the FP-LMTOmethod. Numerical examples of semi-conductors as well as metals are presented. Interbandand intraband transitions are discussed, as are maneto-optical effects. Thechapter ends with a description of the theory of x-ray magnetic circular dichroism,and how its calculation is made possible in the FP-LMTO method.
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| 24. |
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| 25. |
- Wills, John M., et al.
(författare)
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Future Developments and Outlook
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 183-185
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this final chapter a short summary and outlook is presented. In addition,future, anticipated developments of the FP-LMTO method are listed.
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| 26. |
- Wills, John M., et al.
(författare)
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Implementation
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 89-93
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Details of the implementation of the FP-LMTO method are presented in this chapter. This includes programming language, routines for numerical operations like diagonalization and fast Fourier transforms, and parallelization aspects.
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| 27. |
- Wills, John M., et al.
(författare)
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Introduction to Electronic Structure Theory
- 2010
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Ingår i: Springer Series in Solid-State Sciences. - Berlin, Heidelberg : Springer Nature. ; , s. 25-34
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- An introduction to electronic structure theory of solids is presented, including the general form of the one-electron wave function. The evaluation of the electron density, density of states as well as the calculation of energy bands is described. Different types of integration of reciprocal space are presented, and numerical examples given for their accuracy. The calculation of a self-consistent field is also described, as is the Rayleigh-Ritz variational method.
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| 28. |
- Wills, John M., et al.
(författare)
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Introductory Information
- 2010
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Ingår i: Springer Series in Solid-State Sciences. - Berlin, Heidelberg : Springer Nature. ; , s. 3-6
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this introductory chapter a short historical note on the history of linear muffin-tin orbital methods is given, together with general background information and units used throughout the book. The main objectives with the book are presented as well as information about web-based information, which easier enables using the full-potential linear muffin-tin orbitals method.
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| 29. |
- Wills, John M., et al.
(författare)
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Linear Muffin-Tin Orbital Method in the Atomic Sphere Approximation
- 2010
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Ingår i: Springer Series in Solid-State Sciences. - Berlin, Heidelberg : Springer Nature. ; , s. 35-46
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this chapter the linear muffin-tin orbitals (LMTO) are defined, which includes linearization of the radial part of the wave function, the ‘head’ and ‘tails’ of the basis functions, and the so called structure constant. The atomic sphere approximation (ASA) is introduced and a comparison between the Korringa–Kohn– Rostoker (KKR) method and the linear muffin-tin orbital method is made. The advantages and disadvantages of the LMTO-ASA method are discussed.
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| 30. |
- Wills, John M., et al.
(författare)
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Magnetism
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 133-143
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Chapter 12 describes the theory of magnetism, with focus on spin and orbital moments, and the magnetic anisotropy. Numerical examples are presented, both for bulk and surfaces, and the particular symmetry aspects of relativistic oneelectron theory and magnetism are described. The different contributions to the magnetic anisotropy are analyzed, as are the often cumbersome aspects of a slow convergence of the calculation of the magnetic anisotropy with respect to the number of k-points.
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| 31. |
- Wills, John M., et al.
(författare)
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Obtaining RSPt from the Web
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 95-97
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this short chapter details of how to obtain the FP-LMTO code from the web site http://www.rspt.net are given. In addition, a short instruction on how to install the FP-LMTO code is presented.
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| 32. |
- Wills, John M., et al.
(författare)
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The Full-Potential Electronic Structure Problem and RSPt
- 2010
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Ingår i: Full-Potential Electronic Structure Method. - Berlin, Heidelberg : Springer Nature. ; , s. 47-73
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The full-potential methodology is presented in this chapter, with details of how the non-spherical electron density and potential are expanded in the muffintin regions, as well as the interstitial region. Details in the implementation of the full-potential linear muffin-tin orbitals (FP-LMTO) method are presented, with a general definition of the mathematical functions used and the symmetry aspects of these functions. The difference between a minimal, double and triple basis set is described, and numerical tests of the convergence of these basis functions are presented.
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