Rearrangement Of Electronic Structure Research Articles

On the link between the reaction force constant and conceptual DFT.

The reaction force constant ( ), introduced by Professor Alejandro Toro-Labbé, plays a pivotal role in characterizing the reaction pathway by assessing the curvature of the potential energy profile along the intrinsic reaction coordinate. This study establishes a novel link between and the reactivity descriptors of conceptual density functional theory (c-DFT). Specifically, we derive expressions that relate the reaction force constant to nuclear softness and variations in chemical potential. Our findings indicate that regions of the reaction pathway where is negative match with significant electronic structure rearrangements, while positive regions match mostly with geometric rearrangements. This correlation between and c-DFT reactivity descriptors enhances our understanding of the underlying forces driving chemical reactions and offers new perspectives for analyzing reaction mechanisms. The internal reaction path for the proton transfer in SNOH, chemical potential, and nuclear softness were computed using DFT with B3LYP exchange-correlation functional and 6-311++G(d,2p) basis set.

An ultrasensitive electrochemical sensor based on NiFe-LDH-MXene and ruthenium nanoparticles composite for detection of nitrofurantoin in food samples

The excessive use of nitrofurantoin (NFT) represents a threat to ecosystems and food safety, making it necessary to develop efficient and accurate detection methods. Herein, the Ru/NiFe-LDH-MXene/SPCE electrode was successfully synthesized by one-step electrodeposition and employed to the NFT electrochemical sensing. Combining 2D MXenes with multifunctional 2D layered double hydroxides (LDHs) creates synergistic interactions within the MXene-LDH heterostructures, modifying the electrochemical performance. Furthermore, the incorporation of noble metal nanoparticles and nanoclusters can significantly enhance electrochemical performance by promoting favorable interactions at the metal-carrier interface and optimizing the rearrangement of electronic structure. Based on this, the developed Ru/NiFe-LDH-MXene/SPCE sensor demonstrates remarkable sensitivity (152.44 μA μM−1 cm−2) and an ultralow detection limit (2.2 nM). Notably, the sensor was employed for NFT detection in food samples with satisfactory recoveries, making it a promising electrochemical sensor for the detection of NFT.

Symmetry breaking induced local electron rearrangement to enhance photocatalytic tetracycline hydrochloride oxidation and hydrogen evolution of carbon nitride

A symmetry breaking strategy was achieved by a sample doping approach and used to overcome the sluggish carrier transfer and insufficient light capture capacity of carbon nitride photocatalysts. The obtained local electronic structural reconstruction resulted in the generation of an intermediate energy level, which can regulate the band gap structure and boost the redox reaction progress. Furthermore, the DFT calculation results prove the electronic structure rearrangement brings adsorption characteristic changes for H2O and O2 molecules, leading to the variation of free radicals’ generation. Combing the advantages of band gap structure optimization and internal electron rearrangement, the phosphorus doped carbon nitride achieves a balance between light absorption properties and photocatalytic redox capacity, exhibiting stronger reduction capacity, high carrier separation efficiency, and optimized adsorption sites. Consequently, the phosphorus doped carbon nitride shows enhanced activities in photocatalytic tetracycline hydrochloride degradation (3.6-fold increase), peroxydisulfate activation (4.5-fold increase), and hydrogen generation (13.5-fold increase) compared to pristine carbon nitride. This research highlights the symmetry regulation strategy as a promising method for developing highly efficient multifunctional carbon nitride-based photocatalysts.

Ultrafast Charge Relocation Dynamics in Enol-Keto Tautomerization Monitored with a Local Soft-X-ray Probe.

Proton-coupled electron transfer (PCET) is the underlying mechanism governing important reactions ranging from water splitting in photosynthesis to oxygen reduction in hydrogen fuel cells. The interplay of proton and electronic charge distribution motions can vary from sequential to concerted schemes, with elementary steps occurring on ultrafast time scales. We demonstrate with a simulation study that femtosecond soft-X-ray spectroscopy provides key insights into the PCET mechanism of a photoinduced intramolecular enol* → keto* tautomerization reaction. A full quantum treatment of the electronic and nuclear dynamics of 2-(2′-hydroxyphenyl)benzothiazole upon electronic excitation reveals how spectral signatures of local excitations from core to frontier orbitals display the distinctly different stages of charge relocation for the H atom, donating, and accepting sites. Our findings indicate that ultraviolet/X-ray pump-probe spectroscopy provides a unique way to probe ultrafast electronic structure rearrangements in photoinduced chemical reactions essential to understanding the mechanism of PCET.

Magnetic properties of Pb-=SUB=-1-y-=/SUB=-Sc-=SUB=-y-=/SUB=-Te alloys

The magnetic field dependences of the magnetization (B≤9 T, T=2-70 K) of the samples from a single crystal Pb1-yScyTe (y=0.01) ingot, synthesized by the Bridgman method, are studied. It is established that, in accordance with the generally accepted model of the rearrangement of the electronic structure of alloys during doping, there is no paramagnetic contribution of single scandium ions located in the nodes of the metal sublattice in the studied samples. The magnetization of the samples contains several contributions: superparamagnetism of scandium clusters, linear in field diamagnetism of the crystal lattice and the paramagnetism of free electrons, as well as the oscillating contribution of the de Haas--van Alphen effect. The field dependences of the main contribution of scandium clusters are successfully approximated using the Langevin function. The average concentration, magnetic moment and the total magnetic moment of the clusters per unit volume of the sample were determined with an increase in the impurity concentration along the ingot. Keywords: PbTe-based alloys, 3d-transition metal impurities, rearrangement of electronic structure, field dependences of magnetization, superparamagnetism of scandium clusters.

NbSe2 Meets C2N: A 2D‐2D Heterostructure Catalysts as Multifunctional Polysulfide Mediator in Ultra‐Long‐Life Lithium–Sulfur Batteries

AbstractThe shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPS) hamper the practical application of lithium–sulfur batteries (LSBs). Toward overcoming these limitations, herein an in situ grown C2N@NbSe2 heterostructure is presented with remarkable specific surface area, as a Li–S catalyst and LiPS absorber. Density functional theory (DFT) calculations and experimental results comprehensively demonstrate that C2N@NbSe2 is characterized by a suitable electronic structure and charge rearrangement that strongly accelerates the LiPS electrocatalytic conversion. In addition, heterostructured C2N@NbSe2 strongly interacts with LiPS species, confining them at the cathode. As a result, LSBs cathodes based on C2N@NbSe2/S exhibit a high initial capacity of 1545 mAh g−1 at 0.1 C. Even more excitingly, C2N@NbSe2/S cathodes are characterized by impressive cycling stability with only 0.012% capacity decay per cycle after 2000 cycles at 3 C. Even at a sulfur loading of 5.6 mg cm−2, a high areal capacity of 5.65 mAh cm−2 is delivered. These results demonstrate that C2N@NbSe2 heterostructures can act as multifunctional polysulfide mediators to chemically adsorb LiPS, accelerate Li‐ion diffusion, chemically catalyze LiPS conversion, and lower the energy barrier for Li2S precipitation/decomposition, realizing the “adsorption‐diffusion‐conversion” of polysulfides.

Tubular CoFeP@CN as a Mott–Schottky Catalyst with Multiple Adsorption Sites for Robust Lithium−Sulfur Batteries

AbstractThe shuttle effect and the sluggish reaction kinetics of lithium polysulfide (LiPS) seriously compromise the performance of lithium–sulfur batteries (LSBs). To overcome these limitations and enable the fabrication of robust LSBs, here the use of a Mott–Schottky catalyst based on bimetallic phosphide CoFeP nanocrystals supported on carbon nitride tubular nanostructures as sulfur hosts is proposed. Theoretical calculations and experimental data confirm that CoFeP@CN composites are characterized by a suitable electronic structure and charge rearrangement that allows them to act as a Mott–Schottky catalyst to accelerate LiPS conversion. In addition, the tubular geometry of CoFeP@CN composites facilitates the diffusion of Li ions, accommodates volume change during the reaction, and offers abundant lithiophilic/sulfiphilic sites to effectively trap soluble LiPS. Therefore, S@CoFeP@CN electrodes deliver a superior rate performance of 630 mAh g−1 at 5 C, and remarkable cycling stability with 90.44% capacity retention over 700 cycles. Coin cells with high sulfur loading, 4.1 mg cm−2, and pouch cells with 0.1 Ah capacities are further produced to validate their superior cycling stability. In addition, it is demonstrated here that CoFeP@CN hosts greatly alleviate the often overlooked issues of low energy efficiency and serious self‐discharging in LSBs.

Local electronic structure rearrangements and strong anharmonicity in YH3 under pressures up to 180\u2009GPa

The discovery of superconductivity above 250 K at high pressure in LaH10 and the prediction of overcoming the room temperature threshold for superconductivity in YH10 urge for a better understanding of hydrogen interaction mechanisms with the heavy atom sublattice in metal hydrides under high pressure at the atomic scale. Here we use locally sensitive X-ray absorption fine structure spectroscopy (XAFS) to get insight into the nature of phase transitions and the rearrangements of local electronic and crystal structure in archetypal metal hydride YH3 under pressure up to 180 GPa. The combination of the experimental methods allowed us to implement a multiscale length study of YH3: XAFS (short-range), Raman scattering (medium-range) and XRD (long-range). XANES data evidence a strong effect of hydrogen on the density of 4d yttrium states that increases with pressure and EXAFS data evidence a strong anharmonicity, manifested as yttrium atom vibrations in a double-well potential.

Resonant impurity level of Ni in the valence band of Pb1−xSnxTe alloys

The phase and elemental compositions and galvanomagnetic properties (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) of samples from a single-crystal Pb1−x−ySnxNiyTe ingot (x = 0.08, y = 0.01) synthesized by the Bridgman–Stockbarger method were studied. Microscopic inclusions enriched in nickel were found. It is shown that in the main phase, the tin concentration increases exponentially along the ingot (x = 0.06–0.165), while the concentration of nickel impurity does not exceed 0.4 mol %. A significant increase in the concentration of holes along the ingot and an abnormal increase in the Hall coefficient with increasing temperature were found; both are due to the pinning of the Fermi level by the resonant nickel level located in the valence band. The dependences of the hole concentration and of the Fermi energy at T = 4.2 K on the tin concentration in alloys are calculated using the two-band Kane dispersion law. A qualitative model of electronic structure rearrangement is proposed. The model takes into account the movement of the nickel level into the depth of the valence band with an increase in tin concentration and the redistribution of electrons between the valence band and the level. The energy position of the nickel level and the speed of its movement relative to the top of the valence band with an increase in the tin content in Pb1−xSnxTe alloys are estimated.

Effect of scandium doping and of matrix composition variation on galvanomagnetic properties and electronic structure of Pb1-x-ySnxScyTe alloys

We synthesize a single-crystal Pb1-x-ySnxScyTe (x = 0.08, y = 0.02) ingot and investigate the composition and the galvanomagnetic properties of samples cut from it. We find that all samples are single-phase and determine the distribution of tin and scandium along the ingot. As the concentration of scandium increases, we find the p-n-inversion of the conductivity type at the liquid-helium temperature, an increase in the electron concentration, and its saturation at n ≈ 1.0 × 1020 cm−3, indicating the pinning of the Fermi level by the scandium resonant level located well above the bottom of the conduction band. Using the six-band Dimmock dispersion relation, dependences of the Fermi energy on the scandium and tin content are calculated. A diagram of the electronic structure rearrangement of Pb1-x-ySnxScyTe upon increasing tin content is proposed; the energy and the compositional coefficient of the scandium level movement with respect to the band edges are estimated.

Densities of Pt–X (X: Fe, Co, Ni and Cu) binary melts and thermodynamic correlations

The densities of liquid binary Pt–X (X: Fe, Co, Ni and Cu) alloys were measured over a wide temperature range including the supercooled liquid region, using electromagnetic levitation under a static magnetic field. The static magnetic field effectively suppressed translational motion and surface oscillation of the levitated Pt–X sample droplets, enabling high-accuracy density measurement in a non-contact manner. The excess molar volumes (VE) of the liquid alloys were evaluated from the density measurements, and we demonstrated that the liquid Pt–X systems have positive VE with negative excess molar Gibbs energy (GE). The Pt–X systems have the common feature that order–disorder transitions are present in their phase diagrams. It should be also noted that VE decreases and GE increases with increasing number of electrons in the 3d orbital of X. This unique feature in the liquid Pt–X systems was discussed with possible rearrangement of electronic structure caused by alloying Pt with X.

Kinetics of the Variation in the Magnetic Impurity Ion Concentration in Pb1–x–ySn x V y Te Alloys upon Doping

The field and temperature dependences of the magnetization (magnetic fields B ≤ 7.5 T, temperatures T = 2.0–75 K) of samples from a Pb1–x–ySn x V y Te (x = 0.08, y = 0.01) single-crystal ingot synthesized by the Bridgman–Stockbarger method. It is established that the sample magnetization contains two main contributions, notably, the paramagnetism of vanadium ions and diamagnetism of the crystal lattice. The field and temperature dependences of the magnetization are approximated by the sum of modified Brillouin functions corresponding to the paramagnetic contributions of vanadium in two different charge states and the diamagnetic contribution linear in terms of field. The concentrations of vanadium ions in two different magnetic states and the character of their variation along the ingot are determined within the scope of the alloy’s electronic-structure rearrangement because of doping. The results are compared with the data of X-ray fluorescence microanalysis and the results of studying the galvanomagnetic properties of the samples.

Кинетика изменения концентраций магнитных ионов примеси в сплавах Pb-=SUB=-1-x-y-=/SUB=-Sn-=SUB=-x-=/SUB=-V-=SUB=-y-=/SUB=-Te при легировании

AbstractThe field and temperature dependences of the magnetization (magnetic fields B ≤ 7.5 T, temperatures T = 2.0–75 K) of samples from a Pb_1– x – y Sn_ x V_ y Te ( x = 0.08, y = 0.01) single-crystal ingot synthesized by the Bridgman–Stockbarger method. It is established that the sample magnetization contains two main contributions, notably, the paramagnetism of vanadium ions and diamagnetism of the crystal lattice. The field and temperature dependences of the magnetization are approximated by the sum of modified Brillouin functions corresponding to the paramagnetic contributions of vanadium in two different charge states and the diamagnetic contribution linear in terms of field. The concentrations of vanadium ions in two different magnetic states and the character of their variation along the ingot are determined within the scope of the alloy’s electronic-structure rearrangement because of doping. The results are compared with the data of X-ray fluorescence microanalysis and the results of studying the galvanomagnetic properties of the samples.

Magnetic properties of Pb1-x-ySnxVyTe alloys

We study the field and temperature dependences of the magnetization (B≤7.5 T, T=2.0-75 K) of samples from a single crystal Pb1-x-ySnxVyTe (x=0.08, y=0.01) ingot synthesized by the Bridgman method. It is established that the magnetization of the samples contains two main contributions: the Brillouin-type paramagnetism of vanadium ions and the diamagnetism of the crystal lattice. Experimental field and temperature dependences of the magnetization are discussed in the framework of a theoretical model of electronic structure rearrangement in Pb1-x-ySnxVyTe with doping and approximated as the sums of two terms based on the modified Brillouin functions for vanadium ions in the V3+ and V2+ states. The concentrations of magnetically active vanadium ions in two different charge states with increasing impurity concentration along the ingot are determined.

Electronic Structure Rearrangements in Hybrid Ribozyme/Protein Catalysis

We analyzed the electronic structural changes that occur in the reaction cycle of a biological catalyst composed of RNA and protein, and elucidated the dynamical rearrangements of the electronic structure that was obtained from our previous study in which ab initio quantum mechanics/molecular mechanics molecular dynamics simulations were performed. Notable results that we obtained include the generation of a reactive HOMO that is responsible for bond formation in the initial stages of the reaction, and the appearance of a reactive LUMO that is involved in the bond rupture that leads to products. We denote these changes as dynamical induction of the reactive HOMO (DIRH) and LUMO (DIRL), respectively. Interestingly, we also find that the induction of the reactive HOMO is enhanced by the formation of a low-barrier hydrogen bond (LBHB), which, to the best of our knowledge, represents a novel role for LBHBs in enzymatic systems.

Temperature and pressure coefficients of iron resonant impurity level in PbTe

We investigate temperature dependences of galvanomagnetic parameters in weak magnetic fields (4.2 ≤ T ≤ 300 K, B ≤ 0.07 T) in the p-Pb1−yFeyTe alloy from the middle part of the single-crystal ingot, where the Fermi level is pinned by the resonant impurity level lying under the top of the valence band. Experiments are performed under hydrostatic compression up to 10 kbar. Using scanning electron microscopy, we find microscopic inclusions of the secondary phase enriched with iron and show that the main phase is characterized by a good uniformity of the spatial distribution of impurities. A monotonous increase of the free hole concentration at liquid-helium temperature under pressure and anomalous temperature dependences of the Hall coefficient in the whole investigated pressure range are revealed. Experimental results are explained by a model assuming pinning of the Fermi level by the impurity level and a redistribution of electrons between the valence band and impurity states with increasing temperature and under pressure. In the framework of the two-band Kane dispersion law, theoretical temperature dependences of the Hall coefficient under pressure, which are in satisfactory agreement with the experimental ones at low temperatures, are calculated and temperature and pressure coefficients of the iron deep level are determined. Diagrams of the electronic structure rearrangement with increasing temperature for Pb1−yFeyTe at pressures up to 10 kbar are proposed.

Soft electronic structure modulation of surface (thin-film) and bulk (ceramics) morphologies of TiO2-host by Pb-implantation: XPS-and-DFT characterization

The results of combined experimental and theoretical study of substitutional and clustering effects in the structure of Pb-doped TiO2-hosts (bulk ceramics and thin-film morphologies) are presented. Pb-doping of the bulk and thin-film titanium dioxide was made with the help of pulsed ion-implantation without posterior tempering (Electronic Structure Modulation Mode). The X-ray photoelectron spectroscopy (XPS) qualification of core-levels and valence bands and Density-Functional Theory (DFT) calculations were employed in order to study the yielded electronic structure of Pb-ion modulated TiO2 host-matrices. The combined XPS-and-DFT analysis has agreed definitely with the scenario of the implantation stimulated appearance of PbO-like structures in the bulk morphology of TiO2:Pb, whereas in thin-film morphology the PbO2-like structure becomes dominating, essentially contributing weak O/Pb bonding (PbxOy defect clusters). The crucial role of the oxygen hollow-type vacancies for the process of Pb-impurity “insertion” into the structure of bulk TiO2 was pointed out employing DFT-based theoretical background. Both experiment and theory established clearly the final electronic structure re-arrangement of the bulk and thin-film morphologies of TiO2 because of the Pb-modulated deformation and shift of the initial Valence Base-Band Width about 1eV up.

Galvanomagnetic properties and electronic structure of iron-doped PbTe

We synthesize an iron-doped PbTe single-crystal ingot and investigate the phase composition and distribution of the iron impurity along the ingot as well as galvanomagnetic properties in weak magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) of Pb1−yFeyTe alloys. We find microscopic inclusions enriched with iron and regions with a chemical composition close to FeTe in the heavily doped samples, while the iron impurity content in the main phase rises only slightly along the length of the ingot reaching the impurity solubility limit at approximately 0.6 mol. %. Samples from the initial and the middle parts of the ingot are characterized by p-type metal conductivity. An increase of the iron impurity content leads to a decrease in the free hole concentration and to a stabilization of galvanomagnetic parameters due to the pinning of the Fermi level by the iron resonant impurity level EFe lying under the bottom of the valence band (Ev − EFe ≈ 16 meV). In the samples from the end of the ingot, a p-n inversion of the conductivity type and an increase of the free electron concentration along the ingot are revealed despite the impurity solubility limit being reached. The kinetics of changes of charge carrier concentration and of the Fermi energy along the ingot is analyzed in the framework of the six-band Dimmock dispersion relation. A model is proposed for the electronic structure rearrangement of Pb1−yFeyTe with doping, which may also be used for PbTe doped with other transition metals.

Free electron laser-driven ultrafast rearrangement of the electronic structure in Ti.

High-energy density extreme ultraviolet radiation delivered by the FERMI seeded free-electron laser has been used to create an exotic nonequilibrium state of matter in a titanium sample characterized by a highly excited electron subsystem at temperatures in excess of 10 eV and a cold solid-density ion lattice. The obtained transient state has been investigated through ultrafast absorption spectroscopy across the Ti M2,3-edge revealing a drastic rearrangement of the sample electronic structure around the Fermi level occurring on a time scale of about 100 fs.

Selected properties of Pt(111) modified surfaces: A DFT study

Abstract Density functional theory calculations were employed to investigate the electronic properties of a Pt(111) surface modified with foreign atoms. The effects of alloying platinum with molybdenum, palladium, and tin changed the interaction between adsorbate orbital and metal d band. This letter discusses the interaction between metal atoms and adsorbate and its influence on electronic structure rearrangement of the species—changes that must be taken into account to explain the behavior of catalytic systems and sensors. Mo/Pt(111) and Sn/Pt(111) exhibited lower susceptibility to poisoning by CO, compared with pure platinum. Both Pt-based materials are expected to find utility in electrodes for alcohol and hydrogen oxidation.