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Influence of Crystal Structure and 3d Impurities on the Electronic Structure of the Topological Material Cd3As2
摘要： This paper presents a theoretical study of the effects of crystal structure and Mn and Co substitutions for Cd on the electronic structure of the topological material Cd3As2. We have carried out density functional theory calculations of the band structure and density of states in tetragonal and cubic Cd3As2, as well as in Cd3 – xMnxAs2 and Cd3 – xCoxAs2 crystals. The results indicate that the band structure of the cubic Cd3As2 phase differs significantly from that of a Dirac semimetal, characteristic of the tetragonal phase. It has also been shown that, after Co substitution for 1/24 of the Cd atoms, the structure of the density of 3d electron states is similar to that of the density of states in the magnetic semiconductor Cd3 – xMnxAs2, with a characteristic minimum at the Fermi energy. At the same time, in the case of analogous Mn substitution for Cd, the density of d-electron states has no such minimum.
关键词： Mn,density functional theory (DFT) calculations,magnetic semiconductors,topological materials,Co,Cd3As2,Dirac semimetal,band structure,density of states (DOS)
更新于2025-09-10 09:29:36
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Effects of conjugation on the properties of alkynylcarbazole compounds: experimental and theoretical study
摘要： Four novel dyes containing alkynylcarbazole, namely, 2-((9H -carbazol-3-yl)ethynyl)-9-ethyl-9H -carbazole, 3,6-bis((9-ethyl-9H -carbazol-2-yl)ethynyl)-9H -carbazole, 3-(phenylethynyl)-9H -carbazole and 3,6-bis(phenylethynyl)-9H -carbazole, were synthesized on the basis of single and double substitutes by following the Sonogashira coupling method. The synthesized dyes were then assessed as novel photosensitizers in visible-light photopolymerization to evaluate the effects of conjugation on the properties of aromatic compounds. A comparison between UV–vis and TD/DFT electron transition spectra shows that λmax in theoretical ultraviolet spectra matched well with the experimental spectra; every conjugated alkynylcarbazole dye exhibits a wide absorption band in the range of 300–400 mm. Moreover, conjugation enhancement by switching carbazoleacetylene moieties caused a red shift in the absorption bands. The theoretical study showed that the maxima λ of these molecules ranged from ～330 to 370 mm, corresponding to π→π ? and n→π ? electron transitions. Fluorescence spectroscopic data show that the strongest emission peaks exhibit a red shift because of the addition of conjugated acetylene groups. A combination of alkynyl dyes and iodonium under a halogen lamp atmosphere by visible-light photopolymerization displayed a positive response to the cationic polymerization of bisphenol-A epoxy resin A and free-radical polymerization of tripropylene glycol diacrylate.
关键词： photopolymerization,Synthesis,alkynylcarbazole,photosensitizers,DFT calculations
更新于2025-09-10 09:29:36
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Intermediate States Directed Chiral Transfer on a Silver Surface
摘要： Chiral synthesis on surfaces has acquired tremendous interests. We herein report a novel approach of two-dimensional chiral transfer directed by metal-organic intermediate states on a silver surface. With initial deposition at low temperature, the achiral 4,4'-dihydroxybiphenyl molecules self-assemble into large scale two-dimensional networks with four-fold symmetry via intermolecular hydrogen bonding. Fine controlled annealing, however, leads to the formation of tetramer-like chiral metal-organic hybrids, which self-organize into enantiomeric islands on the Ag(100) surface. Subsequent ortho C-C couplings of the reactants lead to dimer products. Of great importance, the chirality expressions of the dimer products are observed to be transferred directly from that of the tetramer intermediate states. The detailed reaction pathways are rationalized by DFT calculations and synchrotron-based XPS experiments, demonstrating the mechanisms of the chiral transfer.
关键词： metal-organic intermediate states,4,4'-dihydroxybiphenyl,DFT calculations,chiral synthesis,synchrotron-based XPS,silver surface,chiral transfer
更新于2025-09-10 09:29:36
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Computational screening of bulk materials with intrinsic intermediate band
摘要： Intermediate band compounds are promising high-efficiency materials for solar cells. Besides that, they also show unusual properties that make them interesting from a fundamental point of view. In this work, we create a series of filters capable of searching the AFLOW-ICSD materials database for compounds that show intrinsic intermediate bands. We analyse all available binary and ternary compounds, totaling 45,656 entries. The selected materials show at least one narrow band (maximum width of 1 eV) next to the energy gap. After removal of repeated entries and of wide bandgap insulators, we end up with a total of 660 materials that present intermediate bands. From this group, the majority has completely empty or filled intermediate bands or, during new calculations, changed to another state with a different type of intermediate band or no band of this type. Nevertheless, three compounds fulfill all criteria and continue to present a partially filled intermediate band (Bi2Rh2O7, Ca5FeN6, and OsTb6I10), showing potential for solar cells applications.
关键词： Intermediate band,Solar cells,Materials screening,High-throughput screening,DFT calculations
更新于2025-09-10 09:29:36
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Trialkylsilyl-Substituted Silole and Germole Dianions
摘要： The synthesis of dipotassio-2,5-bis(trialkylsilyl)-silacyclopentadienediides K2[3] and germacyclopentadienediides K2[4] is reported. The prepared silole dianions, 3, are characterized by a significantly deshielded silicon nuclei with 29Si NMR signals at very unusual low field positions for silicon anions (δ29Si = 148?169). The results of DFT calculations revealed that this deshielding is a consequence of the silylene-like frontier orbitals of silole dianions 3 and efficient hyperconjugation between the trialkylsilyl-substituents and the cyclic delocalized π-system. Solid-state structure determinations of potassium salts of silole and germole dianions revealed a novel polymeric bis-η5,bis-η1-coordination mode between heterole and potassium ions.
关键词： germole dianions,hyperconjugation,polymeric coordination,silole dianions,DFT calculations
更新于2025-09-10 09:29:36
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Reconciling Structural and Spectroscopic Fingerprints of the Oxygen Evolving Complex of Photosystem II: A Computational Study of the S <sub/>2</sub> State
摘要： The catalytic cycle of photosynthetic water oxidation occurs at the Mn4CaO5 oxygen-evolving complex (OEC) of Photosystem II (PSII). Extensive spectroscopic data have been collected on the intermediates, especially the S2 (Kok) state, although the proton and electron inventories (Mn oxidation states) are still uncertain. The “high-oxidation” paradigm, assigns S2 Mn oxidation level (III, IV, IV, IV) or (IV, IV, IV, III), whereas a “low-oxidation” paradigm posits two additional electrons. Here we investigate the geometric (XRD, EXAFS) and spectroscopic (EPR, ENDOR) properties of the S2 state using quantum chemical DFT calculations, focusing on the neglected low paradigm. Two interconvertible electronic spin configurations are predicted as ground states, producing multiline (S = 1/2) and broad (S = 5/2) EPR signals in the low paradigm oxidation state (III, IV, III, III) and with W2 as OH– and O5 as OH–. They have “open” (S = 5/2) and “closed” (S = 1/2) Mn3CaO4-cubane geometries. Other energetically accessible isomers with ground spin states 1/2, 7/2, 9/2, or 11/2 can be obtained through perturbations of hydrogen-bonding networks (e.g. H+ from His337 to O3 or W2), consistent with experimental observations. Conformers with the low oxidation state configuration (III, IV, IV, II) also become energetically accessible when the protonation state is O5 (OH–), W2 (H2O) and neutral His337. The configuration with (III, IV, III, III) agrees well with earlier low temperature EPR and ENDOR interpretations, while the MnII-containing configuration agrees partially with recent ENDOR data. However, the low-oxidation paradigm does not yield isotropic ligand hyperfine interactions in good agreement with observed values. We conclude that the low Mn oxidation state proposal for the OEC can closely fit most of the available structural and electronic data for S2 at accessible energies.
关键词： EPR,low-oxidation paradigm,oxygen-evolving complex,ENDOR,Photosystem II,DFT calculations,S2 state
更新于2025-09-10 09:29:36
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Synthesis, optical characterization, and TD-DFT studies of novel mero/bis-mero cyanine dyes based on N-Bridgehead heterocycles
摘要： Novel mero/bis-mero cyanine dyes based on N-Bridgehead imidazo[1,2-g]quinolino[2,1-a][2,6]naphthyridine have been synthesized and characterized to evaluate intramolecular charge transfer (ICT) effect on the energy gap (E0-0). The UV–Vis/emission spectral studies revealed that, dyes are absorbed in the region of λmax (485-577) nm and emitted at (567-673) nm. Their solvatochromic behavior in solvents of various polarities, viz. (CCl4, C6H6, H2O, CHCl3, acetone, and DMF) was studied to emphasize the effect of solvent polarity on the absorption maxima, molar extinction coefficients of the dyes, and excitation energy of the dyes. Their electron cloud delocalization in HOMO/LUMO levels were studied by DFT using Gaussian 09 software. Time-dependent density functional theory (TD-DFT) was applied to theoretically explore the first excitation energy (E0-0) of these dyes which in well agreement with experimental results.
关键词： TD-DFT calculations,Photo-physical properties,Solvatochromic behavior,Mero cyanine
更新于2025-09-09 09:28:46
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A complete characterization of vibrational IR and Raman spectra of the highly-symmetrical octathia[8]circulene
摘要： The highly-symmetrical octathia[8]circulene molecule (8S) was synthesized and well studied in Moscow, including X-ray diffraction, IR and Raman spectra assignment on the ground of molecular DFT calculation. Nevertheless, this comprehensive study could not explain a big number of interesting deviations from the DFT predictions based on the molecular D8h symmetry restriction being specific for a free species in a gas phase. In present work we have performed DFT optimization of the 8S tetramer starting with the X-ray diffraction analysis of a similar structure. DFT calculation of IR and Raman spectra of such a huge system provides a good assignment of the crystal-field splitting and new band occurrence. The force-field distortions, electric charges and polarizability dependence on the tetramer structure are well reproduced by the B3LYP functional with the dispersion correction. Thus, the small shifts of IR and Raman bands, their splitting and intensity redistribution upon weak intermolecular interactions in crystal packing are explained and full assignment of all observed bands is presented.
关键词： DFT calculations,Davydov splitting,Raman spectra,tetramer,FT-IR spectra,octathia[8]circulene
更新于2025-09-09 09:28:46
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bilayers
摘要： Magnetic exchange coupling behavior was investigated in MnBi/FeCo bilayer system at the hard/soft magnetic interface. We performed a combined study of cross-sectional high resolution transmission electron microscopy (HR-TEM), DFT calculations, and micromagnetic simulations to elucidate effect of interface structure on exchange coupling. Exchange spring MnBi/FexCo1?x (x = 0.65 and 0.35) bilayers with various thicknesses of the soft magnetic layer were deposited in a dc magnetron sputtering unit from alloy targets. According to magnetic measurements, using a Co-rich layer leads to a more coherent exchange coupling with optimum soft layer thickness of about 1 nm. Our DFT calculations predicted formation of a polycrystalline FeCo layer with coexisting crystalline and disordered (110) phases. The indexed FFTs from HR-TEM images con?rmed a crystalline FeCo(110) layer, with slight misorientation in some areas, and a disordered region close to the interface which deteriorates interface exchange coupling. Moreover, our micromagnetic simulations showed how the thickness of the FeCo layer and the interface roughness both control the effectiveness of exchange coupling in MnBi/FeCo bilayer.
关键词： Magnetic exchange coupling,micromagnetic simulations,HR-TEM,MnBi/FeCo bilayer,DFT calculations
更新于2025-09-09 09:28:46
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[ACS Symposium Series] Raman Spectroscopy in the Undergraduate Curriculum Volume 1305 || Solvent Sensitivity of the ?C≡N Group: A Raman Spectroscopic Study
摘要： The cyano or nitrile group, ?C≡N, exhibits a distinct vibrational mode around the 2100–2300 cm-1 region that is highly sensitive to the solvent polarity, hydrogen bonding interactions, and the electric field around it. In this chapter, the solvent sensitivity of the ?C≡N group was studied using Raman spectroscopy. First, the Raman spectra of ?C≡N-containing samples ranging from acetonitrile to nitrile gloves were contrasted. Second, we give an example where the ?C≡N group had an associated pH dependence due to the groups around it. Lastly, we studied the effect of various solvents on the ?C≡N mode. Raman assignments were verified using DFT-based calculations.
关键词： cyano group,DFT calculations,Raman spectroscopy,nitrile group,solvent sensitivity
更新于2025-09-09 09:28:46