On the Ab Initio DFT + U Calculations of the Physical Properties of a Compound with Strong Electron–Electron Correlations by the Case of KFeS2

Kiiamov, Airat; Kuznetsov, Maxim; Batulin, Ruslan; Tayurskiı̆, D. A.

doi:10.1134/s0021364022020023

Cited by 3 publications

(5 citation statements)

References 21 publications

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“…It was mentioned that the magnetic moment of iron ions obtained in [40] is not in agreement with the neutron diffraction experimental results [1]. This may point to the strong delocalization of Fe d-electrons, and the DFT + U approach is necessary for a proper description of the system [40,42].…”

Section: Density Functional Theory Calculations For the Phonon Densit...mentioning

confidence: 83%

“…Indeed, it is well known that GGA + U functionals may underestimate bandgaps, therefore, hybrid functionals [48][49][50][51] or self-interaction-corrected DFT [52,53] techniques have been used to obtain more accurate results. We used a strategy of finding U and J (U = 1.5 eV and J = 2 eV [42]) within the DFT + U route, which provides the experimentally measured magnetic moment per iron ion (1.9 µ B ) and band gap (0.35 eV). Then, the phonon frequencies were calculated from the eigenvalues of the dynamical matrix.…”

Section: Discussionmentioning

confidence: 99%

“…In [42], it was shown that the set of parameters U = 1.5 eV and J = 2 eV (U eff = −0.5 eV) provides a correct description of the magnetic properties (magnetic moment) and electronic properties (bandgap value) of KFeS 2 simultaneously. Thus, the calculations presented in this paper were carried out within the DFT + U scheme with the above-mentioned set of parameters.…”

Section: Density Functional Theory Calculations For the Phonon Densit...mentioning

confidence: 99%

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Density Functional Theory Approach to the Vibrational Properties and Magnetic Specific Heat of the Covalent Chain Antiferromagnet KFeS2

et al. 2022

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Ternary potassium-iron sulfide, KFeS2, belongs to the family of highly anisotropic quasi-one-dimensional antiferromagnets with unusual “anti-Curie–Weiss” susceptibility, quasi-linearly growing with a rising temperature up to 700 K, an almost vanishing magnetic contribution to the specific heat, drastically reduced magnetic moment, etc. While some of the measurements can be satisfactorily described, the deficiency of the entropy changes upon the magnetic transition and the spin state of the iron ion remains a challenge for the further understanding of magnetism. In this work, high-quality single-crystalline samples of KFeS2 were grown by the Bridgman method, and their stoichiometry, crystal structure, and absence of alien magnetic phases were checked, utilizing wave-length dispersive X-ray electron-probe microanalysis, powder X-ray diffraction, and 57Fe Mössbauer spectroscopy, respectively. An ab initio approach was developed to calculate the thermodynamic properties of KFeS2. The element-specific phonon modes and their density of states (PDOS) were calculated applying the density functional theory in the DFT + U version, which explicitly takes into account the on-site Coulomb repulsion U of electrons and their exchange interaction J. The necessary calibration of the frequency scale was carried out by comparison with the experimental iron PDOS derived from the inelastic nuclear scattering experiment. The infrared absorption measurements confirmed the presence of two high-frequency peaks consistent with the calculated PDOS. The calibrated PDOS allowed the calculation of the lattice contribution to the specific heat of KFeS2 by direct summation over the phonon modes without approximations and adjustable parameters. The temperature-dependent magnetic specific heat evaluated by subtraction of the calculated phonon contribution from the experimental specific heat provides a lower boundary for estimating the reduced spin state of the iron ion.

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Section: Density Functional Theory Calculations For the Phonon Densit...mentioning

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Section: Density Functional Theory Calculations For the Phonon Densit...mentioning

confidence: 99%

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Density Functional Theory Approach to the Vibrational Properties and Magnetic Specific Heat of the Covalent Chain Antiferromagnet KFeS2

et al. 2022

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“…The chains are characterized by the short Fe-Fe distance (2.815 Å) [8] not much exceeding the Fe-Fe distance of metallic iron (2.48 Å). Previous neutron diffraction experiments on 1) e-mail: AiratPhD@Gmail.com As was shown in our previous work [9], in order to correctly describe a KFeS 2 crystal in terms of the density functional theory, it is necessary to use the DFT + U approximation. Strongly non-localized states of Fe 3d -electrons cannot be satisfactorily described by the Generalized Gradient Approximation (GGA), and it is necessary to introduce a Hubbard-like correction to take these electrons into account explicitly.…”

mentioning

confidence: 99%

“…Is should be noted that the system under consideration potentially cannot be correctly described in terms of standard non-U DFT approach, and it is necessary to introduce Hubbard-like corrections to system energy functional. So, in the case of magnetically ordered compounds right choice of the Hubbard parameter is necessary for the correct description of magnetic ground state and magnetic moments value [9].…”

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confidence: 99%

Classical Density Functional Theory Approach to the Vibrational Properties and Lattice Specific Heat of a Quasi-One-Dimensional Antiferromagnet KFeSe2

Kuznetsov

Kiiamov²,

Tayurskiı̆³

2022

Jetp Lett.

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We have performed ab-initio calculations of vibrational properties of KFeSe2 compound utilizing density functional theory. Total and element specific phonon densities of states (PDOS) were calculated within a direct approach of harmonic approximation. We used phonon density of states to calculate lattice contribution to the specific heat. The calculated phonon density of states shows numerous of high-frequency vibrational modes of Fe and Se atoms, which strongly restricts application of the Debye model for analysis of thermodynamic properties of KFeSe2. The results of the present paper could be used in a further estimation of magnetic specific heat of KFeSe2.

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Ab initio Modeling of Phonons in the Family of Quasi-One-Dimensional Antiferromagnets AFeX2

Kiiamov,

Kuznetsov,

Tsurkan

et al. 2024

Phonons - Recent Advances, New Perspectives and Applications [Working Title]

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A review of the recent development in ab initio calculations of the vibrational properties of quasi-one-dimensional (1D) antiferromagnets with AFeX2 structure is presented. Density functional theory (DFT + U) was applied to calculate the phonon modes specific to each element in the structure and the corresponding partial density of states (PDOS). The calculations revealed a strongly non-Debye phonon DOS. Using these results, the nuclear inelastic scattering spectra, temperature dependence of the Lamb-Mössbauer factor, infrared (IR) absorption strength, and phonon-specific heat were derived by direct summation over the phonon modes. The calculations demonstrate good agreement with the experiments and pave the way for understanding the anomalous magnetic properties of AFeX2 quasi-one-dimensional antiferromagnets at a quantitative level.

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On the Ab Initio DFT + U Calculations of the Physical Properties of a Compound with Strong Electron–Electron Correlations by the Case of KFeS2

Cited by 3 publications

References 21 publications

Density Functional Theory Approach to the Vibrational Properties and Magnetic Specific Heat of the Covalent Chain Antiferromagnet KFeS2

Density Functional Theory Approach to the Vibrational Properties and Magnetic Specific Heat of the Covalent Chain Antiferromagnet KFeS2

Classical Density Functional Theory Approach to the Vibrational Properties and Lattice Specific Heat of a Quasi-One-Dimensional Antiferromagnet KFeSe2

Ab initio Modeling of Phonons in the Family of Quasi-One-Dimensional Antiferromagnets AFeX2

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