Electronic structure and magnetic properties of solids

Savrasov, S. Y.; Toropova, A.; Katsnelson, M. I.; Lichtenstein, A. I.; Antropov, Vladimir; Kotliar, Gabriel

doi:10.1524/zkri.220.5.473.65072

Cited by 14 publications

(7 citation statements)

References 116 publications

(113 reference statements)

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“…97,98 The variation of the Gruneisen parameter with volume, given by the parameter q, which is usually considered as a constant, shows strong temperature and pressure dependences in our calculations. The calculated static elastic and bulk moduli at ambient temperature are in fairly good agreements with measurements and previous calculations.…”

Section: Discussionmentioning

confidence: 76%

“…Deviations from experiment are probably due to errors in DFT, rather than our methodology, and show the need for inclusion of magnetic fluctuations, such as through DFMT. 97,98 The variation of the Gruneisen parameter with volume, given by the parameter q, which is usually considered as a constant, shows strong temperature and pressure dependences in our calculations.…”

Section: Discussionmentioning

confidence: 76%

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First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures

Sha

Cohen

2010

Phys. Rev. B

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We investigate the equation of state and elastic properties of hcp iron at high pressures and high temperatures using first principles linear response linear-muffin-tin-orbital method in the generalized-gradient approximation. We calculate the Helmholtz free energy as a function of volume, temperature, and volume-conserving strains, including the electronic excitation contributions from band structures and lattice vibrational contributions from quasi-harmonic lattice dynamics. We perform detailed investigations IntroductionIron is one of the most abundant elements in the Earth, and is fundamental to our world. The study of iron at high pressures and high temperatures is of great geophysical interest, since both the Earth's liquid outer core and solid inner core are composed mostly of this element. Although the crystal structure of iron at the extremely high temperature (4000 to 8000 K) and high pressure (330 to 360 GPa) conditions found in the inner core is still under intensive debate, 1-10 the hexagonal-close-packed phase (ε-Fe) is commonly believed to have a wide stability field extending from deep mantle to core conditions, and serves as a starting point for understanding the nature of the inner core. 11 Significant experimental and theoretical efforts have been recently devoted to investigate various properties of hcp iron at high pressures and high temperatures. New high-pressure diamond-anvil-cell techniques have been developed or significantly improved, which makes it possible to reach higher pressures and provide more valuable information on material properties in these extreme states. First-principles based theoretical techniques have been improved in reliability and accuracy, and have been widely used to predicate the high pressure-temperature behavior and provide fundamental understandings to the experiment.Despite intensive investigations, numerous fundamental problems remain unresolved, and many of the current results are mutually inconsistent. 11 The melting line at very high pressures has been one of the most difficult and controversial problems. 12-19Other major problems include possible subsolidus phase transitions 2,4,5,11,20 and the magnetic structure of the dense hexagonal iron. In section II we detail the theoretical methods to perform the first-principles calculations and obtain the thermal properties and elastic moduli. We present the results and related discussions about the thermal equation of state in section III, and about the thermoelasticity in section IV. We conclude with a brief summary in Section V. II. Theoretical methodsThe Helmholtz free energy F for many metals has three major contributionswith V as the volume, T as the temperature, and δ as the strain. E static is the zerotemperature energy of a static lattice, F el is the thermal free energy arising from electronic excitations, and F ph is the lattice vibrational energy contribution. We obtain both E static and F el from first-principles calculations directly, assuming that the eigenvalues for given lattice and nuclear pos...

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Section: Discussionmentioning

confidence: 76%

Section: Discussionmentioning

confidence: 76%

First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures

Sha

Cohen

2010

Phys. Rev. B

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“…74 Both the effect of the choice of the LDA+U scheme on the orbital occupation and subsequent properties like the electronic band gap 75,76 as well as the dependence of the magnetic properties on the value of Hubbard U and Hund exchange J have been analyzed in the literature. [77][78][79] A better scheme for the LDA+U calculations would be to use the full Coulomb matrix with a proper treatment of the double counting issue.…”

Section: U σ1σ2mentioning

confidence: 99%

Ab initiocalculation of the effective on-site Coulomb interaction parameters for half-metallic magnets

et al. 2013

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Correlation effects play an important role in the electronic structure of half-metallic (HM) magnets. In particular, they give rise to non-quasiparticle states above (or below) the Fermi energy at finite temperatures that reduce the spin polarization and, as a consequence, the efficiency of spintronics devices. Employing the constrained random-phase approximation (cRPA) within the full-potential linearized augmented-plane-wave (FLAPW) method using maximally localized Wannier functions, we calculate the strength of the effective on-site Coulomb interaction (Hubbard U and Hund exchange J) between localized electrons in different classes of HM magnets considering: (i) sp-electron ferromagnets in rock-salt structure, (ii) zincblende 3d binary ferromagnets, as well as (iii) ferromagnetic and ferrimagnetic semi-and full-Heusler compounds. For HM sp-electron ferromagnets, the calculated Hubbard U parameters are between 2.7 eV and 3.9 eV, while for transition-metal-based HM compounds they lie between 1.7 and 3.8 eV, being smallest for MnAs (Mn-3d orbitals) and largest for Cr2CoGa (Co-3d orbitals). For the HM full-Heusler compounds, the Hubbard U parameters are comparable to the ones in elementary 3d transition metals, while for semi-Heusler compounds they are slightly smaller. We show that the increase of the Hubbard U with structural complexity, i.e., from MnAs to Cr2CoGa, stems from the screening of the p electrons of the non-magnetic sp atoms. The p-electron screening turns out to be more efficient for MnAs than for Cr2CoGa. The calculated Hubbard U parameters for CrAs, NiMnSb, and Co2MnSi are about two times smaller than previous estimates based on the cLDA method. Furthermore, the width of the correlated d or p bands of the studied compounds is usually smaller than the calculated Hubbard U parameters. Thus, these HM magnets should be classified as weakly correlated materials.

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“…For the linear response calculations we adopted a Green's function formalism within the ASA [9,10]. This technique has been extensively tested and applied to many different metallic and insulating systems [9,11]. A similar method was recently applied to LaFeAsO [12].…”

mentioning

confidence: 99%

Magnetism and exchange coupling in iron pnictides

Pulikkotil¹,

Ke²,

Schilfgaarde³

et al. 2010

Supercond. Sci. Technol.

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Using linear-response density-functional theory, we obtain the magnetic interactions in the several iron pnictides. The ground state has been found to be non-collinear in FeSe, with a large continuum of nearly degenerate states lying very close to the magnetic "striped" structure. The presence of non-collinearity also seems to be a generic feature of iron pnictides when the Fe moment is small. At small RF e−Se the system is itinerant: strong frustration give rise to excess of spin entropy, long ranged interactions create incommensurate orderings and strong biquadratic (or ring) couplings violate the applicability of Heisenberg model. There is a smooth transition to more localized behavior as RF e−Se increases: stable magnetic orbital order develops which favor long range AFM stripe ordering with strongly anisotropic in-plane exchange couplings. The stabilization of the stripe magnetic order is accompanied by the inversion of the exchange coupling.1 Accumulated experimental studies indicate that the recently discovered iron oxyarsenide family (Fe-As-La-O) and iron chalcogenide (Fe-Se) superconductors[1, 2] similar itinerant antiferromagnetic metallic systems. This fact distinguishes these systems from traditional high-T c superconductors where the local-moment picture and the importance of strongly correlated electrons is generally accepted. While the physics of these systems can be dramatically different they share an important common feature: antiferromagnetic (AFM) interactions on a (nearly) 2D lattice. One can hope that these materials have similar physics and analysis of new metallic systems will shed some light on a nature of magnetic fluctuations in both type of superconductors.Description of magnetism in itinerant magnets is rather complicated, owing to the lack of a commonly accepted rigid spin picture and the disappearance of adiabaticity. The trivial use of localized models leads to oversimplification of the physics of itinerant magnets. As we show here, the degree of itineracy is critical to understand the ground states and magnetic excitations in iron pnictides. Owing to a strong competition between on-site Hund energy and Fe-As bonding in iron pnictides [3][4][5], we adopt the local density approximation (LDA) as we believe it to be the most appropriate readily accessible method to describe these systems [6].We analyze the magnetic properties of iron pnictides, using a variety of implementations of the LSDA, including FLAPW, FPLMTO, LMTO-ASA. The latter includes calculations of non-collinear configurations following the original prescription [8]. Full-potential results are in excellent agreement with each other, and (where they can be compared) very similar to those obtained in Ref. [7]. The ASA results are also in reasonably good agreement with them. For the linear response calculations we adopted a Green's function formalism within the ASA [9,10]. This technique has been extensively tested and applied to many different metallic and insulating systems [9,11]. A similar method was recently applied to...

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Electronic structure and magnetic properties of solids

Cited by 14 publications

References 116 publications

First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures

First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures

Ab initiocalculation of the effective on-site Coulomb interaction parameters for half-metallic magnets

Magnetism and exchange coupling in iron pnictides

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