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Importance of electron correlations in understanding photoelectron spectroscopy and Weyl character of
摘要： We study the role of electron correlations in the presumed type-II Weyl semimetallic candidate γ-MoTe2 by employing density functional theory (DFT) where the on-site Coulomb repulsion (Hubbard U) for the Mo 4d states is included within the DFT+U scheme. We show that pure DFT calculations fail to describe important features of the light-polarization dependence of the angular resolved photoemission intensity which can be accounted for by including the role of the Hubbard U. At the same time, while pure DFT calculations cannot explain the angular dependence of the Fermi surface as revealed by quantum oscillation experiments (a fact which had raised doubt about the presence of the Weyl physics in γ-MoTe2), inclusion of such on-site Coulomb repulsion can. We find that while the number of Weyl points (WPs) and their position in the Brillouin zone change as a function of U, a pair of such WPs very close to the Fermi level survive the inclusion of these important corrections. Our calculations suggest that the Fermi surface of γ-MoTe2 is in the vicinity of a correlations-induced Lifshitz transition, which can be probed experimentally and its interplay with the Weyl physics might be intriguing.
关键词： electron correlations,Lifshitz transition,angular resolved photoemission,MoTe2,DFT+U,Hubbard U,quantum oscillation,Weyl semimetal,photoelectron spectroscopy
更新于2025-09-23 15:23:52
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Influence of Oxygen Vacancy Density on the Polaronic Configuration in Rutile
摘要： Polaronic con?gurations that were introduced by oxygen vacancy in rutile TiO2 crystal have been studied by the DFT + U method. It is found that the building block of TiO6 will expand when extra electron is trapped in the central Ti atom as polaron. With manually adjusting the initial geometry of oxygen vacancy structure, a variety of polaronic con?gurations are obtained after variable-cell relaxation. By calculating different sizes of supercell model, it is found that the most stable con?guration can be in?uenced by the density of oxygen vacancy. With increasing interaction between vacancies, the most stable polaronic con?guration change from small polaronic con?guration to mixed con?guration.
关键词： DFT + U,rutile,electronic structure,oxygen vacancies,polarons
更新于2025-09-10 09:29:36
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First-Principles Insights into the Oxidation States and Electronic Structures of Ceria-Based Binary, Ternary and Quaternary Oxides
摘要： Ceria and ceria-based materials have versatile technological and industrial applications, physically ascribed to the flexible fluctuation of Ce oxidation state between Ce4+ and Ce3+. A considerable multi-disciplinary research has been spent to obtain Ce oxidation state, the crucial quantity regarding the application; however, a rigorous and physically correct determination of oxidation state is still lacking. Here we conduct first-principles DFT + U calculations to unambiguously determine the physical oxidation state of Ce in ceria-based materials such as the homogenous CenO2n-2 (n = 7, 9, 10, 11, 12), ceria doped by multivalent Ti and V, Ce-Ti(V)-O ternary compounds, and Ce-Ti-V-O quaternary compounds. The results show that Ce oxidation state depends on the local structure and chemical surrounding: Oxygen vacancy facilitates the transition from Ce4+ to Ce3+, consistent with the localization of Ce 4f electrons; Ti and V with the 3d energy levels higher than 4f energy levels of Ce generally tend to reduce Ce4+ to Ce3+ particularly under the oxygen-deficiency condition. The atom-resolved determination of Ce oxidation states in the complicated compounds offers great promise for understanding the physical and chemical behavior of ceria-based materials, and for rational design of novel ceria-based materials for application potentials.
关键词： Ceria-based materials,First-principles calculations,Electronic structures,DFT + U,Oxidation states
更新于2025-09-04 15:30:14