Electronic Structure Of Transition Metals Research Articles

Tunable electronic structure and optical properties of GaN monolayer via substituted doping and strain

In this study, the stability, optical properties and electronic structure of transition metal (TM) (Cr, Mn, Fe) doped GaN monolayers is investigated within the first-principles calculation methods. Additionally, the influence of biaxial strain on the aforementioned system is explored. The results demonstrate that substitutional doping effectively adjusts the electronic structure of GaN monolayer, enhancing its performance. The TM-doped GaN monolayer structures exhibit strong dynamic stability: doping with Cr and Fe bring magnetic properties, while Mn doping results in a half-metallicity property. In terms of optical absorption, the GaN:Mn system exhibits significant absorption in the infrared region, while GaN:Cr and GaN:Fe systems show stronger absorption in the visible light and ultraviolet regions compared to the pristine GaN monolayer. Under the biaxial strain from −3% to +12%, with increments of 3%, the band gap types of GaN:Cr, GaN:Fe, and GaN:Mn systems undergo minimal changes, with gradual reduction in gap values. Meanwhile, the optical absorption of doped systems exhibits systematic growth and redshift, particularly evident in the infrared-visible-ultraviolet spectral regions for the GaN:Mn system. These results indicate the controllability and variability of two-dimensional GaN materials, providing new avenues for the potential use of GaN as a material for optoelectronic devices.

Optimizing Nickel Orbital Occupancy via Co‐Modulation of Core and Shell Structures to Accelerate Alkaline Hydrogen Electro‐Oxidation Reaction

AbstractNickel‐based catalysts are recognized as a promising alternative to platinum‐based catalysts for the alkaline hydrogen oxidation reaction (HOR) yet suffer from poor stability and relatively low activity. Herein, a nitrogen ligand‐assisted approach is reported to encapsulate nickel‐copper nanoparticles within few carbon layers, and by modulating the core and shell components/structure, the charge distribution in the nanostructures can be finely regulated. The optimized Ni93Cu7@NC catalyst exhibits outstanding HOR activity with an intrinsic activity of 61.0 µA cm−2 and excellent stability, which is among the most advanced Ni‐based HOR catalysts. Notably, an alkaline exchange membrane fuel cell utilizing this catalyst achieves a peak power density of 381 mW cm−2 and maintains stability at 100 mA cm−2 for over 24 h. Experimental and theoretical investigations unveil that the electron re‐distribution at the interface of NiCu core and nitrogen‐doped carbon reduces the electron occupancy in Ni 4s‐H 1s bonding orbitals and Ni 3dz2/yz‐O 2p antibonding orbitals, leading to a weakened hydrogen binding energy and enhance hydroxide binding energy. Consequently, the limiting energy for the HOR is reduced following a bifunctional mechanism on the Ni93Cu7@NC. This work provides a core‐shell co‐modulation strategy to accurately regulate the electronic structure of transition metals to design robust catalysts.

Three-dimensional biotemplate-loaded nickel sulfide vacancies engineered to promote the absorption of electromagnetic waves.

Vacancy engineering offers an appealing strategy for modifying the electronic structure of transition metals. Transition metals with abundant sulfur vacancies can significantly contribute to the microwave absorption capabilities of absorbers. In this study, an NixSy@De composite material was synthesized through a straightforward hydrothermal synthesis technique. The effective absorption bandwidth (EAB) of this composite material reached 9.86 GHz at 1.44 mm. A minimum reflection loss (RLmin) of -33.61 dB at 1 mm was achieved, and after mild etching, the RLmin further improved to -93.53 dB at 1.16 mm to achieve a high-attenuation microwave absorption. The exceptional performance of NixSy@De for the absorption of electromagnetic waves (EMWs) is based on its high dielectric loss, substantial magnetic loss, and excellent impedance matching. This work combines transition metal sulfides with three-dimensional biotemplated diatomite, providing valuable insights into the design of advanced EMW absorbing materials.

The Electronic Structure of Transition Metal (TM) Oxides for the Oxygen Evolution Reaction: The Critical Role of TM 3d Hole State

Electrolysis of water to produce hydrogen and oxygen is a promising pathway for the storage of renewable energy in form of chemical fuels. The efficiency of the overall process is usually limited by the sluggish kinetics of the oxygen evolution reaction (OER) due to a complex four-electron/proton transfer mechanism. Therefore, the most crucial step for water electrolysis to become a widespread industrial process is to develop efficient electrocatalysts capable of driving the OER at a low overpotential.[1,2] In this talk, I will summaries the key electronic features that induces high catalytic activity towards the oxygen evolution reaction of trivalent transition metal (TM) oxides with perovskite structure, such as LaCoO3 [3] and LaFeO3.[4] The partial substitution of La for Sr in LaTMO3 results in the oxidation of TM3+ to TM4+ and substantially enhances OER catalytic activity. A comprehensive X-ray spectroscopic study, based on in-situ XPS and XAS, reveals a strong correlation of the enhanced OER catalytic activity with the presence of cations in the 4+ oxidation state. Increasing the concentration of TM cations in the 4+ oxidation state leads to a more covalent TM–O bond due to higher TM 3d–O 2p orbital hybridization and shifts the energy position of the valence band (VB) closer to the Fermi level (E F). Such an electronic modulation optimizes the surface adsorption energetics of *OH intermediates, contributing to faster OER kinetics. Furthermore, the oxidation of TM3+ to TM4+ creates a new unoccupied state (hole state) below the conduction band, associated with the formation of TM 3d empty electronic states. This hole states reduce the energy barrier for electron transfer associated with the OER, as illustrated in the figure below, thereby facilitating charge transfer at the interface during the reaction.Figure 1: Key electronic features of transition metal (TM) oxides for the oxygen evolution reaction

Lab-Scale X-Ray Emission/Absorption Spectroscopy for Operando Measurement of Electronic Structure of Transition Metals in Battery Electrodes

Tracking the change in electronic structure of target elements is crucial to investigate the nature of redox reactions occurring in battery electrodes. X-ray emission spectroscopy (XES) and x-ray absorption fine structure (XAFS) perform this role well with high sensitivity and throughput, but the requisite of synchrotron facilities often limits those availability for material characterization.Using a lab-scale x-ray emission/absorption spectrometer, we investigated the changes in the local structure and chemistry around the 3d transition metal elements of LiMO2 cathodes for Li-ion batteries as a function of the battery state of charge (SoC). Ex situ measurement was prepared from the electrode samples with discrete difference in SoC. Coupled with ex situ measurement, operando measurement was performed using pouch cells with LiMO2 cathode, which enabled a real-time monitoring of chemical shift in an element-specific manner resulted from changing electrode potential.Through the XES mode of the bench-top spectrometer, fluorescence emissions from the LiMO2 cathode, or the cell containing it, was monochromatized by a spherically bent crystal analyzer (SBCA). The Kβ emissions of 3d transition metal elements such as cobalt display position/shape difference of spectrum with varying SoC. The trend of chemical shift and change in spectral features provided the information on the electronic structure variation, such as oxidation state change of 3d transition metals in LiMO2 during charge and discharge (i.e., delithiation and lithiation). Furthermore, valence-to-core (VtC) emission signals helped enable in-depth analysis such as spin structure characterization.In addition to the XES analysis, we could measure K-edge XAFS for the same 3d transition metals in LiMO2 as well. In the XAFS mode of the spectrometer, SBCA monochromatized bremsstrahlung x-ray generated from a high-power x-ray tube is used to make an incident source energy-dispersive. While Kβ XES probed occupied levels, K-edge XAFS examined unoccupied levels providing comprehensive understanding on the change in electronic structure of 3d transition metals in LiMO2. Figure 1

Borophene-supported single transition metal atoms as potential oxygen evolution/reduction electrocatalysts: a density functional theory study.

Due to the maximal atom utilization, high activity, and selectivity, the two-dimensional (2D) matrix supported single-atom catalysts (SACs) have attracted substantial research interests. In this work, we carried out the theoretical study on the stability, activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), and its dependence on the electronic structure of transition metal (TM) anchored on two types of borophene (called β12 and χ3) by density functional theory (DFT) calculations. The results show that the early- and VIII-TM anchored β12 and χ3 borophenes are structurally and thermodynamically stable. The overpotentials of OER (ηOER) over the Ni supported on β12 and χ3 borophene SACs, designated as β12-Ni and χ3-Ni, are 0.38 and 0.35V, respectively. The ηORR of β12-Ni and χ3-Ni are estimated to be as low as 0.34 and 0.39V, respectively. The OER/ORR activity of the SACs can be well correlated with their electronic structures. The high ηOER values of early TM supported on borophene SACs correspond to high d-band center of TM. Both β12-Ni and χ3-Ni have a moderate d-band center. Since the overpotentials for OER and ORR on β12-Ni and χ3-Ni are comparable to those of Pt group metals and their oxides, β12-Ni and χ3-Ni can be considered as the promising bifunctional catalysts for OER and ORR.

Tailoring the Electronic Structure of Transition Metals by the V2C MXene Support: Excellent Oxygen Reduction Performance Triggered by Metal–Support Interactions

The enhancement of oxygen reduction reaction (ORR) activity can significantly boost the performance of fuel cells. MXene-supported transition metals with strong metal-support interactions (SMSI) are an effective strategy to increase the catalytic activity and durability while decreasing the usage of noble metals. Herein, a series of composites of transition-metal atoms (Ni, Pd, Pt, Cu, Ag, and Au) deposited on V2C MXene are designed as potential catalysts for ORR using density functional theory. The calculation results demonstrate that all the transition metals prefer to form a monolayer on V2C (TMML/V2C) with high thermodynamic stability because of SMSI, in which the Pd, Pt, Ag, and Au monolayers exhibit high chemical stability during the ORR process. PtML/V2C exhibits the highest activity toward ORR with the overpotential down to 0.38 V and the largest energy barrier of 0.48 eV. The excellent catalytic performance originates from the modification of the electronic structure by the V2C support because of SMSI. Our studies elucidate the SMSI between transition-metal atoms and V2C MXene from the atomic level and thus rationally design the ORR catalyst at the cathode of fuel cells to enhance the activity while possessing high stability and less Pt usage.

Tuning the electronic structure of transition metals embedded in nitrogen-doped graphene for electrocatalytic nitrogen reduction: a first-principles study.

As one of the most important subjects in chemistry, nitrogen activation and reduction to yield ammonia is still a big challenge. The lack of deep understanding of the nitrogen reduction reaction (NRR) impedes the development of high-performance catalysts. In the present study, we introduce a second transition metal (M = Mn, Fe, Co, Ni, Cu, Zn, and Mo) into the active site of a single-atom Fe-N-C catalyst to tune the electronic structure and study the activity of the as-designed neighboring bimetal Fe/M-N-C catalyst in the electrochemical NRR under acidic conditions, by performing first-principles calculations. By checking the stability of the catalysts, the adsorption ability for N2, the Gibbs free energy change for the potential-determining step in the NRR, and the hydrogen evolution reaction (HER) activity, only the Fe/Mn-N-C catalyst is predicted to be a promising candidate for the NRR as it shows significantly improved catalytic activity and strong selectivity against the HER. A mechanistic study reveals the synergistic effects of the bimetal active sites, and the introduced Mn atom generates a strong multi-reference effect on the electronic configuration to create more tunnels to transfer the d-orbital electrons to activate the inert N[triple bond, length as m-dash]N triple bond, inducing the "acceptance-donation" process to facilitate the activation and reduction of N2. The current results provide an effective strategy to design stable, active, and selective catalysts for the electrochemical NRR.

Unraveling the Role of Al Substitution in Anionic Oxygen Activity of Ni-Rich Layered Oxide Cathodes

Ni-based layered oxides have attracted great attention for the development of high energy and high capacity Li-ion cathodes. The most popular Ni-based cathodes, LiNi x Mn y Co1-x-y O2 (NMC) and LiNi x Co y Al1-x-y O2 (NMC), are indeed derivatives of LiNiO2 by partially substituting Ni with Co, Mn or Al. The current trend to develop high-Ni and low-Co or Co-free layered Ni-based oxide cathodes, makes a strong push to the limit of Ni content in such layered oxides, leading to many common properties with their parent compound, LiNiO2. In fact, lithium nickel oxide often exists off-stoichiometry because of the presence of Ni2+ in the Li layer, which blocks the Li+ diffusion pathway upon lithiation/delithiation. Therefore, a second metal of a minimal content, such as Co or Al, which can somehow facilitate the formation of layered structure is still needed, although they are not strongly favored due to cost and sacrifice upon the use of inactive Al. In this work, a number of Al substituted lithium nickel oxides, LiAl x Ni1-x O2 (0 ≤ x ≤ 0.20), have been synthesized via a solid state reaction, showing good R m layered structure. Along with their parent LiNiO2, the oxygen activity in these compounds have been studied using combined synchrotron X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) and differential electrochemical mass spectrometry (DEMS). The goal of this research is to elucidate the role of Al on the anionic oxygen activity in Ni-based layered oxides, including both reversible anionic oxygen redox and irreversible oxygen release during the electrochemical process. The electronic structure of transition metal and O was investigated at different states of charge to obtain a complete picture of cationic and anionic redox during the charge/discharge process. Beyond the redox chemistry, the effect of Al substitution on the phase transformation at highly delithiated states, dominated by H2 to H3 phase transformation for LiNiO2, as well as thermal stability was carefully studied. We hope this work helps provide a comprehensive picture of the role of Al substitution on the overall performance of Ni-based layered oxide cathodes.

Variational Relativistic Two-Component Complete-Active-Space Self-Consistent Field Method.

The accurate description of the electronic structure of transition metals and their compounds can be complicated by both the large number of close-lying states that often have multiconfigurational nature and significant relativistic effects. In order to address these challenges we present a two-component complete-active-space self-consistent field method that includes scalar relativistic effects and one-electron spin-orbit coupling during the self-consistent wave function optimization procedure. These relativistic effects are included via an "exact two-component" transformation of the solution of the one-electron modified Dirac equation. The method is applied to the study of spin-orbit splitting of ground and low-lying excited states of main group elements and selected transition metals.

MOF-Based Nano-Cuboids Electrocatalyst for OER-HER Reactions

Recently, metal organic framework (MOF) derived catalysts, typically synthesized using precursors consisting of transition metals and organic linkers, have emerged as promising active and inexpensive electrocatalysts due to their intrinsic advantages of high porosity, three-dimensional structures, and compositional flexibility. In particular, MOFs with organic ligands containing carbon, nitrogen, and sulfur atoms coordinated to transition metal centers have been reported to form three dimensional and uniformly porous structures, resulting in considerably increased active surface area and enhanced physical properties.[1-5] These MOFs, often composed of transition metal atoms such as nickel, cobalt, and iron, and heteroatoms such as nitrogen, sulfur, and phosphorus, are characterized by strong interactions between them[6,7], which can serve as electrocatalytically active sites for HER and OER. The advantages of MOF-derived active materials in advanced energy conversion and storage applications have been recently highlighted as efficient electrocatalysts for fuel cells, metal-air batteries, and electrolyzers. For example, Gadipelli et al. recently reported a design route for the synthesis of MOF-derived electrocatalysts, in which zeolitic imidazolate framework (ZIF) was used as the template. The resulting MOF catalyst containing active Co-N-C species demonstrated efficient ORR and OER activities. Yu et al. reported an active OER electrocatalyst based on porous carbon coated nickel phosphides (NiP) prepared using Ni-based PBA nanoplates as a template. The structural advantages of MOFs allowed NiP catalyst to demonstrate superior electrocatalytic activity towards OER compared to NiO and Ni(OH)2 counterparts. Despite these electrocatalyst developments, however, bi-functional MOF-derived electrocatalysts active towards both HER and OER for water-splitting application have rarely been reported to the best of our knowledge. In this study, we introduce novel MOF containing Ni-Co-Fe transition metal centers, denoted NCF-MOF, as a dual-function water-splitting catalyst for enhancing HER and OER activities. The morphology of the catalyst is revealed to exhibit nano-cuboid structure with multiple meso- and micro-sized pores prepared via a facile synthesis procedure. As MOF catalyst precursors, transition metal-based PBA nanocubes with a chemical formula Mx II[My III(CN)6]z▪H2O, where MII and MIII are divalent and trivalent transition metal cations, respectively, have selected to obtain unique structure and composition of NCF-MOF multi-hollow nano-cuboids. Specifically, PBA nanocube precursors containing nickel, cobalt, and iron have been utilized to maintain the general nano-cuboidal structure, while optimizing the composition of transition metal centers for efficient OER and HER activities. This makes NCF-MOF one of the most promising non-precious electrocatalysts for water-splitting applications in various ways; (i) significantly extended active surface area with high porosity, (ii) formation of active nitrogen species during facile synthesis, and (iii) optimized electronic structure of transition metals for electrocatalysis via oxidation state control. These main electrocatalytic contributors that affect OER and HER have been successfully obtained through careful selection of PBA precursors and the facile synthesis procedure. Furthermore, excellent electrochemical stability has been realized NCF-MOF catalyst which is also attributed to high uniformity of porous nano-cuboidal structure which allow rapid charge transfer and transport of active species. The dual-function of the catalyst and its stability has been confirmed by three-electrode half-cell evaluations, as well as nickel-foam loaded active electrodes for practical demonstrations as efficient and stable References [1] A. Mahmood, W. Guo, H. Tabassum and R. Zou, Adv. Energy Mater., 2016. [2] Z. Li, M. Shao, L. Zhou, R. Zhang, C. Zhang, M. Wei, D. G. Evans and X. Duan, Adv. Mater., 2016, 28, 2337-2344. [3] B. Y. Xia, Y. Yan, N. Li, H. B. Wu, X. W. Lou and X. Wang, Nat. Energy, 2016, 1, 15006. [4] X. Y. Yu, L. Yu, H. B. Wu and X. W. Lou, Angew. Chem. Int. Ed., 2015, 54, 5331-5335. [5] L. Han, X. Y. Yu and X. W. Lou, Adv. Mater., 2016, 28, 4601-4605. [6] T. Y. Ma, S. Dai, M. Jaroniec and S. Z. Qiao, J. Am. Chem. Soc., 2014, 136, 13925-13931. [7] X. F. Lu, P. Q. Liao, J. W. Wang, J. X. Wu, X. W. Chen, C. T. He, J. P. Zhang, G. R. Li and X. M. Chen, J. Am. Chem. Soc., 2016, 138, 8336-8339. Figure 1

Electronic structure of transitional metal doped two dimensional 1T-TaS2: A first-principles study

The electronic structure of transition metal (TM) doped monolayer 1T-TaS2 has been investigated by first-principles calculations. The binding energy of TM-doped TaS2 changes from 1.75 for Nb to 15.49 eV for W, where the distortion rates of bond length for S-TM and Ta-TM are in the range of 0.77%–9.35% and 0.90%–8.87%, respectively. Whether TM doped or not, Fermi level goes across the conduction band. However, an energy gap appears between the conduction and valence bands when Mo, Tc, Ru, Rh, Pd, Ag and Cd are doped. The band gaps are 0.34, 0.53, 0.45 and 0.31 eV in Mo, Ru, Rh and Ag-doped systems, and the spin splittings at M point are 0.21, 0.09, 0.15 and 0.15 eV. The density of states near Fermi level of TM-doped 1T-TaS2 partially comes from TM d orbits, where Tc, Ru, Rh, Pd, Ag and Cd dopants make Ta dxy, dx2-y2, dxz, dyz, dz2 as the main factors at Fermi level. Our results may bring new breakthrough for spintronics.

Structural and Electronic Descriptors of Catalytic Activity of Graphene-Based Materials: First-Principles Theoretical Analysis.

Characteristic features of the d-band in electronic structure of transition metals are quite effective as descriptors of their catalytic activity toward oxygen reduction reaction (ORR). With the promise of graphene-based materials to replace precious metal catalysts, descriptors of their chemical activity are much needed. Here, a site-specific electronic descriptor is proposed based on the pz (π) orbital occupancy and its contribution to electronic states at the Fermi level. Simple structural descriptors are identified, and a linear predictive model is developed to precisely estimate adsorption free energies of OH (ΔGOH ) at various sites of doped graphene, and it is demonstrated through prediction of the most optimal site for catalysis of ORR. These structural descriptors, essentially the number of ortho, meta, and para sites of N/B-doped graphene sheet, can be extended to other doped sp2 hybridized systems, and greatly reduce the computational effort in estimating ΔGOH and site-specific catalytic activity.

An insight into the effects of B-site transition metals on the activity, activation effect and stability of perovskite oxygen electrodes for solid oxide electrolysis cells

Here, effects of B-site transition metals (TMs) in the (La0.6Sr0.4)XO3-δ (X = Mn, Fe, Co) perovskite structure on the activity and stability of the oxygen electrodes during high temperature electrolysis are discussed to provide a deep understanding of the phenomena observed for different oxygen electrodes under anodic polarizations. Performance and stability of the electrodes vary significantly at 800 °C as the TMs changed from Mn to Fe and Co, which is attributed to the different ionic conductivities and surface chemistry of the materials that have a strong dependence on the valence state and electronic structure of TMs. Under an anodic current passage of 200 mA cm−2 at 800 °C, electrode polarization resistance (RE) and overpotential (η) of the (La0.6Sr0.4)MnO3-δ (LSM) electrode decrease significantly by 1.75 Ω cm2 and 101 mV during the 1200 min test, compared with the constant values of RE and η for the (La0.6Sr0.4)FeO3-δ (LSF) and (La0.6Sr0.4)CoO3-δ (LSC) electrodes, an indication of the influence of B-site TMs on the electrode performance and stability. Most serious degradation is observed at the (La0.6Sr0.4)MnO3-δ electrode due to the electrode detachment arising from the accelerated SrO surface segregation and related disintegration of LSM particles near the electrode/electrolyte interface.

The Investigation of Electronic Structure of Transition Metal Doped TiO2 for Diluted Magnetic Semiconductor Applications: A First Principle Study

Although titanium dioxide (TiO2) is a non-magnetic semiconductor material nevertheless it can be transformed into a magnetic semiconductor material, i.e. diluted magnetic semiconductor (DMS), by adding impurities which have magnetic properties. Transition metals are good candidate impurities to be added to TiO2 to form a DMS. This paper reports our investigations on the trends of electronic structure and magnetic properties of TiO2 based DMS with transition metals impurities (Sc, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) by using density functional theory (DFT). TiO2-Fe and TiO2-Mn have big magnetic moment, with the values are about 4.21 Bohr Mag/cell and 3.48 Bohr Mag/cell, respectively. However, based on density of states, TiO2-Sc and TiO2-Ni have no change the magnetic characteristic of pure TiO2. Based on the magnetic and semiconductor properties, the candidates for DMS are TiO2-V, TiO2-Cr,TiO2-Mn, TiO2-Fe, and TiO2-Co system.

Tunable electronic structure of monolayer semiconductor g-C2N by adsorbing transition metals: A first-principles study

The electronic structure of transition metal (TM) adsorbed two-dimensional g-C2N is investigated by first-principles calculations. Most of TM-adsorbed g-C2N show metallic properties, but Ni and Zn adsorptions show a band gap of 0.6 and 1.6 eV. The maximum spin splitting of TM-adsorbed g-C2N from Sc to Zn is 110, 186, 117, 100, 0, 515, 147, 64, 95 and 0 meV, respectively. The magnetic moments of adsorbed structure from Sc to Co are in the range from 0.15 to 2.11 μB, while in Ni, Cu and Zn adsorbed cases no magnetic moments appear. In Fe-adsorbed g-C2N, the adsorption structure at site of Fe12 generates a 90 meV band gap, where the adsorption sites at CC and CN rings are marked as Fe1 and Fe2. The maximum spin splitting is 515, 412 and 750 meV as Fe atomic concentration is 5.56%, 11.11% and 16.67%. Our results can bring more significant basis on the design of spintronic and valleytronic devices.

Electronic structure of transition metal ions in GaN and AlN: Comparing GGA+U with experiment

Electronic structure of Cr, Mn, Fe, and Co transition metal (TM) ions in GaN and AlN is studied within the Generalized Gradient Approximation augmented by the +U corrections, which are treated as free parameters. The main impact of U(N) is the opening of the band gap by shifting both valence and conduction band energies. The intracenter transitions between the gap states of TM impurities are weakly affected by U(N), but they are sensitive to U(TM) which directly act on d(TM) orbitals. The impact of U(TM) depends on both the level symmetry and its occupancy (i.e., on the charge state of the TM ions). Degeneracies of partially occupied multiplet levels are lifted, the effect being mainly driven by the +U correction and not by the Jahn-Teller mechanism. The role of the U-induced hybridization between TM and host states is elucidated.A comparison with experimental intracenter optical transition energies demonstrate that the best agreement is obtained for U ≈ 0 for Fe, and even negative U ≈ −1 eV for Mn. The linear response calculations give U(TM)≈3.5–4.0 eV, which leads to severe discrepancies of about 1 eV with experiment. Importantly, the results obtained with U(Fe) = U(Mn) = U(N) = 5 eV are very close to those obtained with hybrid functionals, but the discrepancies with experiment are even larger. Comparison of the results for GaN and AlN shows that relative energies of gap levels of a given TM ion in the two hosts, as well as their dependencies on U(TM), are the same to within ∼0.2 eV. The estimated valence band offset between GaN and AlN is about 0.5 eV, in agreement with experiment.

Quantum-chemical modeling of strength of organometallic bonds in oil

Metal–organics bond dissociation energies in compounds modeling different metal-containing structures in oil have been calculated using ab initio quantum-chemical methods. It has been found that bond energies calculated by the cbs-qb3, b3lyp/dgdzvp, and b3lyp/cc-pVDZ methods for diatomic molecules are arranged in the order: E(M–O) > E(M–S), E(M–C) > E(M–N), where M = V, Ni, or Co. Vanadium oxide VO in the vanadyl porphyrin molecule has been shown to possess the strongest bond (277.4 kcal/mol). Sandwiched structures are also stable: by using the ub3lyp/6-31g(d,p) method, the decomposition energy of the sandwich (C5H5)2M = M + 2C5H5 has been estimated and equals at 260.2 kcal/mol for M = Fe or 141.0 kcal/mol for M = Ni. The electronic structure of transition metal (M = V, Ni, Fe) complexes with π-conjugated bonds of benzene, pyrrole, and pyridine molecules has been calculated using the ub3lyp/6-31g(d) method. The thermal stability of the complexes has been discussed in terms of bond energy.

Operando soft x-ray emission spectroscopy of LiMn2O4 thin film involving Li–ion extraction/insertion reaction

We developed an electrochemical in situ cell for soft x-ray emission spectroscopy (XES) to accurately investigate the redox reaction and electronic structure of transition metals in the cathode materials for Li–ion battery. The in situ cell consists of a Li–metal counter electrode, an organic electrolyte solution, and a cathode on a membrane window which separates the liquid electrolyte from high vacuum and can pass the incoming and emitted photons. In this study, the Mn 3d electronic structure of LiMn2O4 thin-film electrode was clarified by the operando XES. At the charged state, the XES spectrum changed significantly from the open-circuit-voltage (OCV) state, suggesting oxidation of the Mn3+ component through Li–ion extraction. Upon discharge up to 3.0V vs. Li/Li+, the XES spectrum almost returned to its profile at the OCV state with small difference, indicating the valence change of Mn: Mn3.6+→Mn4+→Mn3.3+ corresponding to the OCV, charged, and discharged states.

Metal-based drugs.

Metals have been considered for millennia to have medicinal values. With the advent of modern medicine, many metal-based drugs have proven to be highly effective in the clinic. Many different metal ions have shown activity against a range of diseases. The unique electronic structure of transition metals offers great versatility, not always seen in organic drugs, in terms of the ability to tune the properties of a given molecule. This review gives a brief overview of the most established therapeutic metals, and their more common applications, such as platinum-based anticancer drugs. New developments within the field of metallodrugs and novel strategies being employed to improve methods of delivery, are also discussed.