NiO: Correlated Bandstructure of a Charge-Transfer Insulator

The bandstructure of the prototypical charge-transfer insulator NiO is computed by using a combination of an {\it ab initio} bandstructure method and the dynamical mean-field theory with a quantum Monte-Carlo impurity solver. Employing a Hamiltonian which includes both Ni-d and O-p orbitals we find excellent agreement with the energy bands determined from angle-resolved photoemission spectroscopy. This solves a long-standing problem in solid state theory. Most notably we obtain the low-energy Zhang-Rice bands with strongly k-dependent orbital character discussed previously in the context of low-energy model theories.Comment: 4 pages, 3 figur

Effect of Electron Correlations on the Electronic Structure and Magnetic Properties of the Full Heusler Alloy Mn2NiAl

In this theoretical study, we investigate the effect of electron correlations on the electronic structure and magnetic properties of the full Heusler alloy Mn (Formula presented.) NiAl in the framework of first-principles calculations. We investigate the electron correlation effect as employed within hybrid functional (HSE) and also within the DFT+U method with varied values of parameters between 0.9 and 6 eV. The XA-crystal structure was investigated with antiferromagnetic orderings of the magnetic moments of the manganese. It was found that with a growth of the Coulomb interaction parameter, the manganese ions magnetic moment increases, and it reaches the value of 4.15–4.46 (Formula presented.) per Mn. In addition, the total magnetic moment decreases because of the AFM ordering of the Mn ions and a small magnetic moment of Ni. The calculated total magnetic value agrees well with recent experiments demonstrating a low value of magnetization. This experimental value is most closely reproduced for the moderate values of the Coulomb parameter, also calculated in constrained LDA, while previous DFT studies substantially overestimated this value. It is also worth noticing that for all values of the Coulomb interaction parameter, this compound remains metallic in its electronic structure in agreement with transport measurements. © 2023 by the authors.Russian Academy of Sciences, РАН; Russian Science Foundation, RSF: 22-22-20109The research was supported by the Russian Science Foundation, project no. 22-22-20109 (https://rscf.ru/en/project/22-22-20109/, M.N. Mikheev Institute of Metal Physics of Ural Branch of Russian Academy of Sciences)

Composition-Induced Magnetic Transition in GdMn1-xTixSi Intermetallic Compounds for x = 0–1

Magnetic intermetallic compounds based on rare earth elements and 3d transition metals are widely investigated due to the functionality of their physical properties and their variety of possible applications. In this work, we investigated the features of the electronic structure and magnetic properties of ternary intermetallic compounds based on gadolinium GdMn1-xTixSi, in the framework of the DFT + U method. Analysis of the densities of electronic states and magnetic moments of ions in Ti-doped GdMnSi showed a significant change in the magnetic properties depending on the contents of Mn and Ti. Together with the magnetic moment, an increase in the density of electronic states at the Fermi energy was found in almost all GdMn1-xTixSi compositions, which may indicate a significant change in the transport properties of intermetallic compounds. Together with the expected Curie temperatures above 300 K, the revealed changes in the magnetic characteristics and electronic structure make the GdMn1-xTixSi intermetallic system promising for use in microelectronic applications. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was supported by the Russian Science Foundation (project no. 18-72-10098) for the electronic structure calculations in Section 3.2. The results of Section 3.1 (antiferromagnetic ordering calculations) were obtained within the state assignment of the Ministry of Science and Higher Education of the Russian Federation (theme “Electron” no. AAAA-A18-118020190098-5)

Correlation effects in Ni 3d states of LaNiPO

The electronic structure of the new superconducting material LaNiPO experimentally probed by soft X-ray spectroscopy and theoretically calculated by the combination of local density approximation with Dynamical Mean-Field Theory (LDA+DMFT) are compared herein. We have measured the Ni L2,3 X-ray emission (XES) and absorption (XAS) spectra which probe the occupied and unoccupied the Ni 3d states, respectively. In LaNiPO, the Ni 3d states are strongly renormalized by dynamical correlations and shifted about 1.5 eV lower in the valence band than the corresponding Fe 3d states in LaFeAsO. We further obtain a lower Hubbard band at -9 eV below the Fermi level in LaNiPO which bears striking resemblance to the lower Hubbard band in the correlated oxide NiO, while no such band is observed in LaFeAsO. These results are also supported by the intensity ratio between the transition metal L2 and L3 bands measured experimentally to be higher in LaNiPO than in LaFeAsO, indicating the presence of the stronger electron correlations in the Ni 3d states in LaNiPO in comparison with the Fe 3d states in LaFeAsO. These findings are in accordance with resonantly excited transition metal L3 X-ray emission spectra which probe occupied metal 3d-states and show the appearance of the lower Hubbard band in LaNiPO and NiO and its absence in LaFeAsO.Comment: 6 pages, 5 figure

Effect of Doping on the Electronic Structure of the Earth’s Lower Mantle Compounds: FeXO3 with X = C, Al, Si

The effect of the mutual doping of C, Si, and Al atoms on the electronic structure and magnetic properties of FeXO3 (X = C, Al, Si) compounds, which are constituent compounds of the Earth’s lower mantle, was studied. In our first principles calculations, it was found that doping with carbon for both FeSiO3 and FeAlO3 leads to the transition of the compound from a semi-metallic state to a metallic one. The values of the magnetic moments of Fe were obtained for pure and doped compounds. For the doped compounds, there is a tendency of the Fe magnetic moment to increase with the growth in the number of substituted ions in the case of replacing Si with C and Si for Al; on the contrary, in the case of replacing Al with C and Si, a decrease in the magnetic moment was revealed. For FeXO3 (X = C, Al, Si), the obtained magnetic moment values were found to be in a good agreement with the known experimental data. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was supported by the Russian Science Foundation (project No. 19-72-30043) for the electronic structure calculations in Section 3, and the magnetic values (Section 4) were obtained within the state assignment of the Ministry of Science and Higher Education of the Russian Federation (theme “Electron” No. AAAA-A18-118020190098-5)

Orbital densities functional

Local density approximation (LDA) to the density functional theory (DFT) has continuous derivative of total energy as a number of electrons function and continuous exchange-correlation potential, while in exact DFT both should be discontinuous as number of electrons goes through an integer value. We propose orbital densities functional (ODF) (with orbitals defined as Wannier functions) that by construction obeys this discontinuity condition. By its variation one-electron equations are obtained with potential in the form of projection operator. The operator increases a separation between occupied and empty bands thus curing LDA deficiency of energy gap value systematic underestimation. Orbital densities functional minimization gives ground state orbital and total electron densities. The ODF expression for the energy of orbital densities fluctuations around the ground state values defines ODF fluctuation Hamiltonian that allows to treat correlation effects. Dynamical mean-field theory (DMFT) was used to solve this Hamiltonian with quantum Monte Carlo (QMC) method for effective impurity problem. We have applied ODF method to the problem of metal-insulator transition in lanthanum trihydride LaH_{3-x}. In LDA calculations ground state of this material is metallic for all values of hydrogen nonstoichiometry x while experimentally the system is insulating for x < 0.3. ODF method gave paramagnetic insulator solution for LaH_3 and LaH_{2.75} but metallic state for LaH_{2.5}.Comment: 35 pages, 5 figure

Electronic structure, magnetic and optical properties of intermetallic compounds R2Fe17 (R=Pr,Gd)

In this paper we report comprehensive experimental and theoretical investigation of magnetic and electronic properties of the intermetallic compounds Pr2Fe17 and Gd2Fe17. For the first time electronic structure of these two systems was probed by optical measurements in the spectral range of 0.22-15 micrometers. On top of that charge carriers parameters (plasma frequency and relaxation frequency) and optical conductivity s(w) were determined. Self-consistent spin-resolved bandstructure calculations within the conventional LSDA+U method were performed. Theoretical interpetation of the experimental s(w) dispersions indicates transitions between 3d and 4p states of Fe ions to be the biggest ones. Qualitatively the line shape of the theoretical optical conductivity coincides well with our experimental data. Calculated by LSDA+U method magnetic moments per formula unit are found to be in good agreement with observed experimental values of saturation magnetization.Comment: 16 pages, 5 figures, 1 tabl

Local Correlations and Hole Doping in NiO: A Dynamical Mean-Field Study

Using a combination of ab initio band-structure methods and dynamical mean-field theory, we study the single-particle spectrum of the prototypical charge-transfer insulator NiO. Good agreement with photoemission and inverse-photoemission spectra is obtained for both stoichiometric and hole-doped systems. In spite of a large Ni d spectral weight at the top of the valence band, the doped holes are found to occupy mainly the ligand p orbitals. Moreover, high hole doping leads to a significant reconstruction of the single-particle spectrum accompanied by a filling of the correlation gap. © 2007 The American Physical Society.We thank W. E. Pickett and R. T. Scalettar for numerous discussions at the early stage of the code development. J.K. was sponsored by the Alexander von Humboldt Foundation. J.K. and D.V. acknowledge partial support by the SFB 484 of the Deutsche Forschungsgemeinschaft. V.J.A. and A.V.L. were supported by the Russian Foundation for Basic Research under Grants No. RFFI-06-02-81017, No. RFFI-04-02-16096, and No. RFFI-03-02-39024 and by the Netherlands Organization for Scientific Research through NWO 047.016.005. A.V.L. acknowledges support from the Dynasty Foundation and International Center

Nature of the Electronic States Involved in the Chemical Bonding and Superconductivity at High Pressure in SnO

We have investigated the electronic structure and the Fermi surface of SnO using density functional theory calculations within recently proposed exchange-correlation potential (PBE + mBJ) at ambient conditions and high pressures up to 19.3 GPa where superconductivity was observed. It was found that the Sn valence states (5s, 5p, and 5d are strongly hybridized with the O 2p states, and that our density functional theory calculations are in good agreement with O K-edge X-ray spectroscopy measurements for both occupied and empty states. It was demonstrated that the metallic states appearing under pressure in the semiconducting gap stem due to the transformation of the weakly hybridized O 2p-Sn 5sp subband corresponding to the lowest valence state of Sn in SnO. We discuss the nature of the electronic states involved in chemical bonding and formation of the hole and electron pockets with nesting as a possible way to superconductivity. © 2011 Pleiades Publishing, Ltd.We acknowledge the support of the Russian Foundation for Basic Research (project nos. 11-02-00022, 10-02-00046, and 10-02-00546), the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Research Chair program, the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (project no. MK 3376.2011.2), the Russian Federal Agency of Science and Innovation (project no. 02.740.11.0217), partial support of the Ministry of Education of Science of the Russian Federation (project no. 2.1.1/779, program “Development of Sci entific Potential of Universities”), and the Russian Federal Agency of Science and Innovation (project no. 02.740.11.0217)

MAGNETIC TRANSITION IN THE 3D SUBLATTICE OF GdMn1-XTiXSi FOR X = 0 - 1

erties of ternary intermetallic compounds based on gadolinium, namely, GdMn1-xTixSi for x ranging from 0 to 1, in the framework of the DFT based approach accounting for strong elec-tronic correlations in Gd.Исследование выполнено при финансовой поддержке гранта Российского Научного Фонда (проект № 18-72-10098)