Valence Electron Density Research Articles

Time-Resolved Chiral X-Ray Photoelectron Spectroscopy with Transiently Enhanced Atomic Site Selectivity: A Free-Electron Laser Investigation of Electronically Excited Fenchone Enantiomers

Chirality is widespread in nature, playing a fundamental role in biochemical processes and in the origin of life itself. The observation of dynamics in chiral molecules is crucial for the understanding and control of the chiral activity of photoexcited states. One of the most promising techniques for the study of photoexcited chiral systems is time-resolved photoelectron circular dichroism (TR-PECD), which offers an intense and sensitive probe for vibronic and geometric molecular structure as well as electronic structures, and their evolution on a femtosecond timescale. However, the nonlocal character of the PECD effect, which is imprinted during the electron scattering off the molecule, makes the interpretation of TR-PECD experiments challenging. In this respect, core photoionization is known to allow site and chemical sensitivity to photelectron spectroscopy. Here we demonstrate that TR-PECD utilizing core-level photoemission enables probing the chiral electronic structure and its relaxation dynamics with atomic site sensitivity. Following UV pumped excitation to a 3s Rydberg state, fenchone enantiomers (C10H16O) were probed on a femtosecond scale using circularly polarized soft x-ray light pulses provided by the free-electron laser FERMI. C 1s binding energy shifts caused by the redistribution of valence electron density in this 3s-valence-Rydberg excitation allowed us to measure transient PECD chiral responses with an enhanced C atom site selectivity compared to that achievable in the ground state molecule. This chemical-specific, site-specific, and enantiosensitive observation of the electronic structure of a transiently photoexcited chiral molecule is expected to pave the way toward chiral femtochemistry probed by core-level photoemission.Received 2 March 2022Revised 27 September 2022Accepted 2 February 2023DOI:https://doi.org/10.1103/PhysRevX.13.011044Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasChiralityElectronic structure of atoms & moleculesPhysical SystemsMoleculesTechniquesPhotoionizationUltrafast femtosecond pump probeX-ray photoelectron spectroscopyAtomic, Molecular & Optical

Double-Heterostructured Nickel Phosphate-Phosphides as High-Activity Electrocatalyst for Ammonia Borane Electrooxidation.

The direct electrooxidation reaction of ammonia borane (ABOR) as the anodic reaction of direct ammonia borane fuel cells (DABFCs) is greatly dependent on the properties of electrocatalysts. Both the active sites and charge/mass transfer characteristics are the key to promoting the processes of kinetics and thermodynamics, which can further improve the electrocatalytic activity. Hence, the catalyst double-heterostructured Ni2 P/Ni2 P2 O7 /Ni12 P5 (d-NPO/NP) with the optimistic redistribution of electrons and active sites is prepared for the first time. The d-NPO/NP-750 catalyst obtained after pyrolysis at 750°C shows the outstanding electrocatalytic activity toward ABOR with an onset potential of -0.329V vs RHE which is better than all the published catalysts. The density functional theory (DFT) computations illustrate that the Ni2 P2 O7 /Ni2 P acts as the activity enhancement heterostructure with a high d-band center (-1.60eV) and the low activation energy barrier, while the Ni2 P2 O7 /Ni12 P5 acts as the conductivity enhancement heterostructure with the highest density of valence electrons.

Analysis of interaction between dislocation and interface of aluminum matrix/second phase from electronic behavior

• Difficulty in dislocation movement at interface is studied by electron transport • Change in valence electrons density at α-Al/second phase interface is calculated • Differential charge density at α-Al/second phase interfaces is analyzed • Inhibitory effect of α-Al/second phase interface on dislocation were studied The inhibitory effect of the second phase on dislocation movement has long been deemed as a great contribution to the strengthening of alloys. We investigate the electronic behavior at the α-Al matrix/second phase interface to explore its inhibitory effect on dislocation movement. This work focuses on the difficulty in dislocation movement on the interface of α-Al/Al 3 Sc, α-Al/θ'(Al 2 Cu), and α-Al/T 1 (Al 2 CuLi) of aluminum-lithium-scandium alloy based on detailed transmission electron microscopy investigation and electron transport calculation. The more drastic the electron transport between two atoms at the interface, the more intense the interaction between them, corresponding to the larger difficulty in breaking and forming bonds between them during the movement process of the extra half plane of dislocation on the interface. The calculated difference in density of valence electrons and differential charge density at α-Al/second phase interface reveals that Al 3 Sc is characterized by the largest resistance to dislocation movement compared to θ'(Al 2 Cu) and T 1 (Al 2 CuLi). The large differential charge density between the interface of (1 0 0) Al3Sc /(1 0 0) Al demonstrates the strong bonds between α-Al and Al 3 Sc and the large difficulty for the extra half plane of dislocation to form or break bonds during the movement process at α-Al/Al 3 Sc interface. The dislocation pile-up indicates a discernible hindering effect of the α-Al/Al 3 Sc interface on dislocation movement. The hindering effect presented by α-Al/Al 3 Sc interface is favorable for the tensile strength.

An Anomalous Electron Configuration Among 3d Transition Metal Atoms

AbstractPhysical properties of materials are mainly determined by valence electron configurations, where different valence shells would induce divergent phenomena. In compounds containing Sc2+, 3d electron occupancy is expected, the same as other transition metal atoms like Ti3+. But this situation still awaits experimental verification in inorganic materials. Here, we selected ScS to measure the valence electron density and orbital population of Sc2+ through delicate quantitative convergent‐beam electron diffraction. With the absence of 3d orbital features around Sc‐atom sites and the nearly bare population of t2g orbital, the unintuitive occupation of 4s orbital in Sc2+ is concluded. It should be the first time to report such a special electron configuration in a transition metal compound, in which 4s rather than 3d orbital is preferred. Our findings reveal the distinct behavior of Sc and probable ways to modulate material properties by controlling electron orbitals.

An Anomalous Electron Configuration Among 3d Transition Metal Atoms.

Physical properties of materials are mainly determined by valence electron configurations, where different valence shells would induce divergent phenomena. In compounds containing Sc2+ , 3d electron occupancy is expected, the same as other transition metal atoms like Ti3+ . But this situation still awaits experimental verification in inorganic materials. Here, we selected ScS to measure the valence electron density and orbital population of Sc2+ through delicate quantitative convergent-beam electron diffraction. With the absence of 3d orbital features around Sc-atom sites and the nearly bare population of t2g orbital, the unintuitive occupation of 4s orbital in Sc2+ is concluded. It should be the first time to report such a special electron configuration in a transition metal compound, in which 4s rather than 3d orbital is preferred. Our findings reveal the distinct behavior of Sc and probable ways to modulate material properties by controlling electron orbitals.

Effects of Cu, Ag and Au on electronic and optical properties of α-Ga2O3 oxide according to first-principles calculations

Ga2O3 is a promising semiconductor material, but, improving its electronic and optical properties is important for the development of semiconductor materials. To improve the electronic and optical properties, we used the first-principles calculations to study the effects of alloying elements on the electronic and optical properties of α-Ga2O3. Three alloying elements comprising Cu, Ag and Au were considered. The results showed that the Cu-doped α-Ga2O3 has greatly stability compared with Ag and Au doped α-Ga2O3. These alloying elements can expand the volume and lattice of α-Ga2O3 because of the discrepancy in the valence electronic density. Importantly, we calculated the directional band gap of α-Ga2O3 as 2.970 eV. It should be noted that the band gap calculated for the transition metal-doped α-Ga2O3 is smaller than that for the parent α-Ga2O3 because adding the alloying element changes the electronic balance between the Ga atom and O atom near the Fermi level. This result demonstrates the ultraviolet properties of α-Ga2O3. However, adding alloying elements (Cu, Ag and Au) leads to migration from the ultraviolet region to the visible light region. In particular, these alloying elements can improve the storage optical properties of the parent Ga2O3.

Bypassing backmapping: Coarse-grained electronic property distributions using heteroscedastic Gaussian processes.

We employ deep kernel learning electronic coarse-graining (DKL-ECG) with approximate Gaussian processes as a flexible and scalable framework for learning heteroscedastic electronic property distributions as a smooth function of coarse-grained (CG) configuration. The appropriateness of the Gaussian prior on predictive CG property distributions is justified as a function of CG model resolution by examining the statistics of target distributions. The certainties of predictive CG distributions are shown to be limited by CG model resolution with DKL-ECG predictive noise converging to the intrinsic physical noise induced by the CG mapping operator for multiple chemistries. Further analysis of the resolution dependence of learned CG property distributions allows for the identification of CG mapping operators that capture CG degrees of freedom with strong electron-phonon coupling. We further demonstrate the ability to construct the exact quantum chemical valence electronic density of states (EDOS), including behavior in the tails of the EDOS, from an entirely CG model by combining iterative Boltzmann inversion and DKL-ECG. DKL-ECG provides a means of learning CG distributions of all-atom properties that are traditionally "lost" in CG model development, introducing a promising methodological alternative to backmapping algorithms commonly employed to recover all-atom property distributions from CG simulations.

First-principles investigation of the effect of noble metals on the electronic and optical properties of GaN nitride

To improve the electronic and optical properties of GaN nitride, here, the effect of four noble metals (Ag, Au, Ir and Pt) on the electronic and optical properties of GaN is studied by the first-principles calculations. The calculated result shows that the Ir-doped GaN has better stability compared to the other noble metal doping. It is found that these noble metals lead to the lattice expansion and volume expansion of GaN due to the discrepancy of valence electronic density. The calculated band gap of GaN is 1.651 eV. However, these noble metals doped GaN (except for Ir-doping) shows metallic behavior because the noble metal gives rise in N-2p state migration from the conduction band to the valence band. Importantly, the result demonstrates the ultraviolet properties of GaN. In particular, the additive noble metals result in absorption coefficient migration from the ultraviolet region to the visible light. As mentioned above, this work can open up a new path to improve the electronic and optical properties of GaN nitride.

Inheritance factor on the physical properties in metallic glasses

Material genetic engineering can significantly accelerate the development of new materials. As an important topic in material science and condensed matter physics, the development of metallic glasses (MGs) with specific properties has largely been the result of trial and error since their discovery in 1960. Yet, property design based on the physical parameters of constituent elements of MGs remains a huge challenge owing to the lack of an understanding of the property inheritance from constitute elements to the resultant alloys. In this work, we report the inherent relationships of the yield strength σ y, Young’s modulus E, and shear Modulus G with the valence electron density. More importantly, we reveal that the electronic density of states (EDOSs) at the Fermi surface (E F) is an inheritance factor for the physical properties of MGs. The physical properties of MGs are inherited from the specific element with the largest coefficient of electronic specific heat (γi ), which dominates the value of the EDOS at E F. This work not only contributes to the understanding of property inheritances but also guides the design of novel MGs with specific properties based on material genetic engineering.

Probing the structural evolution and its impact on magnetic properties of FeCoNi(AlMn)x high-entropy alloy at the nanoscale

We report the first nanoscale investigation of FeCoNi(AlMn) x high-entropy alloys (HEAs) processed by laser metal deposition. The structural evolution of the alloy upon chemical composition variation (0.2 ≤ x ≤ 1.5) was investigated by combining imaging and spectroscopies in (scanning) transmission electron microscopy (S)TEM with density functional theory (DFT). A gradual change from a face-centered cubic (FCC) towards an ordered full-Heusler (L2 1 ) phase by increasing the Al and Mn contents was observed. Direct imaging and atomic-scale calculations revealed a nanoscale interplay between B2 and L2 1 ordered structures for x = 1.5, wherein the latter, Al and Mn occupy two different Wyckoff sites. By decreasing x, the FCC phase dominates exhibiting intense phase separation tendency, ordering phenomena, and nano-precipitation. Although not chemically discriminated, plasmon-peak splitting in low-loss electron energy loss spectra revealed the presence of two valence electron densities within the FCC phase. Lorentz TEM showed that the ordered nano-precipitates and nano-sized grains with a structure based on a tripled FCC unit cell are pinning-sites for magnetic domain walls and dislocations. All alloy compositions exhibited soft-magnetic behavior with coercivity ( H c ) values< 1000 A/m. The FeCoNi(AlMn) 1.5 alloy with L2 1 /B2 nanostructure showed the highest magnetization ( M s ) with relatively low H c , attributed to the large magnetic moment of Mn and the synergistic effect of Mn-Al according to DFT, whilst ordering does not impose a negative effect. Phase separation trends within the FCC phase seem to decrease the M s however, the overall impact on the magnetic behavior is not intense, opening up for new avenues for tuning FeCoNiAlMn properties through chemically-designed phase decomposition regimes. • First nanoscale investigation of FeCoNi(AlMn)x HEAs processed by LMD, combining advanced (S)TEM and DFT calculations. • Ordering phenomena - nanoscale interplay between B2 and L21, ordered superstructures - and impact on magnetic properties. • Atomic site occupancy resolved by direct imaging and atomic-scale calculations. • Phase separation in FCC opens up avenues for tuning alloy properties through chemically-designed decomposition regimes. • All alloy compositions exhibited soft-magnetic behavior with coercivity values< 1000 A/m.

Effectiveness electronic density‐based descriptor to index hard–hard interaction

AbstractWe attempt to introduce the effectiveness electronic density (EED) based on the ratio of the valence and the atomic electrons to measure the contribution of the valence electronic density in an atom. The valence density plays a substantial role in polarizability, the latter being inversely related to the hardness. In the present work, we suggest the EED, found to be, inversely related to the polarizability as a descriptor to identify the hard–hard interaction. This approach is tested and validated on typical reactions such as protonation and deprotonation processes to address the chemical reactivity of the molecular system from the hardness/softness concepts. The results obtained are found to be in good agreement with experimental and chemical behaviour.

放射光X線単結晶X線回折による価電子密度分布解析

The valence electron density distribution in crystals can be observed with high accuracy by precise electron density analysis using the core differential Fourier synthesis （CDFS） method with high-intensity and high-resolution single crystal X-ray diffraction data obtained at a large synchrotron radiation facility; SPring-8. By observing the spatial distribution of electron density proportional to the square of the wave function, the quantum parameters of the orbital states of can be directly determined. Using this method, not only orbital ordered states and bonding electrons but also degenerate orbital states can be directly observed, which may lead to a new method for structural properties research beyond the conventional structural analysis.

Pyrimidine-assisted synthesis of S, N-codoped few-layered graphene for highly efficient hydrogen peroxide production in acid

H 2 O 2 production by electroreduction of oxygen is an attractive alternative to replace the current complex anthraquinone method. However, it is still challenging to realize efficient electrochemical H 2 O 2 production in acid by using cost-effective catalysts. Herein, we report a pyrimidine-assisted chemical-vapor-deposition method to synthesize sulfur-and-nitrogen-codoped few-layered graphene (SNGL) with exceptional activity and selectivity for two-electron oxygen reduction reaction (2e − ORR) in acidic electrolyte (pH = 1). The H 2 O 2 selectivity reaches 90%–100% over a potential range of 0.20–0.55 V, and the maximum H 2 O 2 production rate (4.8 mol g −1 ·h −1 ) exceeds all of the reported H 2 O 2 production performance for carbon-material-based catalysts. Experiments and density functional theory (DFT) simulations reveal that the synergy effect of the combined oxidized sulfur and pyridinic N functional motif can lower the Fermi level of valence electronic states of active edge carbon sites and thus leads to suitable binding strength of ∗OOH intermediate for high selectivity and performance 2e − ORR for H 2 O 2 formation. • Pyrimidine mediates to form S, N-codoped few-layered graphene (SNGL) catalysts • The SNGL catalyst performed a recorded H 2 O 2 production rate • XAS evidences the valence electronic modification for oxygen-adsorption optimization • DFT simulation identified the potential catalytic active sites As one of the 100 most important chemicals in the world, hydrogen peroxide (H 2 O 2 ) is mainly produced by the energy- and waste-intensive anthraquinone oxidation (AO) method. Replacing the AO method with a more environmentally benign electrochemical two-electron oxygen reduction reaction (2e − ORR) depends on low-cost and efficient catalysts. However, metal-free, carbon-based catalyst as a promising candidate behaves encouragingly only under neutral or alkaline conditions, where H 2 O 2 is unstable for collection or unfavorable for linking applications, i.e., the e -Fenton reaction. Herein, we developed a pyrimidine-mediated synthetic method to synthesize S, N-codoped few-layered graphene (SNGL) with surface electronic property optimization, which significantly boosts 2e − ORR in acid. Our work not only created an efficient carbon-based catalyst for H 2 O 2 production in acid but also provided a useful electronic property optimization route for future tuning of carbon-based materials catalysts. A pyrimidine-assisted synthetic method is developed to synthesize sulfur-and-nitrogen-codoped few-layered graphene (SNGL) with optimized valence electronic density for efficient H 2 O 2 electrosynthesis in acid.

Computational Prediction of Graphdiyne-Supported Three-Atom Single-Cluster Catalysts

Computational Prediction of Graphdiyne-Supported Three-Atom Single-Cluster Catalysts

Compton profile and charge density reconstruction by the maximum entropy method

The aim of this work is to propose a theoretical procedure to determine the electron momentum density and Compton profile of valence electrons in solids. The procedure consists in a hybrid methodology that combines the maximum entropy method and Dirac-Hartree–Fock formalism, which allows including exchange and correlation effects on valence electrons for distances near the atomic nucleus and that are approximated using the Breit-Wigner distribution function. This technique can be applied for a wide range of crystalline solids. The results and comparisons reported here are for: lithium, beryllium, aluminum, silicon and copper. The application of the model only requires prior knowledge of the Fermi momentum values. In addition, a reconstruction of the valence electron charge density distribution via simple expression of the Compton profile is derived.

Intercalation of Li Atoms in TaSe2 Film's Anode with LiClO4/PEO Polymer Electrolyte: First Principles Calculation

Using the methods of electron density functional and pseudopotential from the first principles, the total energy, energy reliefs and migration barriers of Li atoms in the interlayer space of layers of anode material made of 2H-TaSe2, 2H-TaSe2 with molecules of polymer electrolytes LiClO4, PEO and LiClO4/PEO, charges on Se atoms limit the interlayer space2H-TaSe2, spatial distributions of valence electron density and their cross sections.

Ordered structure and mechanical properties of ternary Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys under high pressure

The structural and mechanical properties of ScB2 and Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys are investigated in the pressure range of 0–150 GPa based on density functional theory. The ground state structures of ScB2 are screened out by structural substitution, and the P6/mmm is determined as the initial structure of alloying research according to structural stability. The structures of alloy generation and recognition (SAGAR) code combined with first-principles calculations selected the stable structures of Sc0.5TM0.5B2 (TM = Ti, V) and Sc0.5Zr0.5B2 alloys as ordered structure types Ⅰ and Ⅱ, respectively. The formation enthalpy, phonon dispersion and elastic constants demonstrate that Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys are thermodynamically, dynamically and mechanically stable. In the whole pressure range, the elastic moduli of Sc0.5TM0.5B2 (TM = Ti, V, Zr) increased significantly compared with ScB2. This indicates that the introduction of TM improves the mechanical properties of ScB2. The Vickers hardness (HV) of the ScB2 ground state is 42.4 GPa, and the HV of the Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys are increased to 47.8, 50.3 and 44.8 GPa, respectively. The electronic structures and chemical bonding reveal that the Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys have stronger B–B, B–TM covalent bonds, charge interaction, and higher valence electron density, which significantly improves the hardness. The results show that ScB2 and Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys are potential superhard multifunctional materials.

Validation of hybrid WC1LYP functional for ferroelectric LiNbO3 and LiTaO3 using Compton spectroscopy and first-principles computations

Electronic structure and theoretical momentum densities (EMDs) of LiNbO3 and LiTaO3 using linear combination of atomic orbitals (LCAO) scheme are deduced. Present energy bands and density of states using local density approximation, generalised gradient approximation and hybrid (HF + DFT) PBE0 and WC1LYP schemes show a direct band gap (varying between 3.13- 5.13 eV and 3.11–5.18 eV for LiNbO3 and LiTaO3, respectively) at Γ point of Brillouin zones. The WC1LYP hybrid functional based EMDs depict reasonable agreement with present experimental Compton lines (using 100 mCi Am-241 γ-ray Compton spectrometer) than other investigated exchange-correlation potentials, thereby suggesting the applicability of hybrid model like WC1LYP in such ferroelectrics. Accuracy of energy bands is also ensured via electronic and optical properties using modified Becke–Johnson potential as facilitated in the full-potential linearized augmented plane wave method. Presently reported UV–vis measurements for optical band gaps are in consonance with the hybrid potential (WC1LYP) for the both ferroelectrics, which further confirms usefulness of hybrid scheme. Moreover, equal–valence–electron–density scaled experimental data reveal more covalent character of LiNbO3 than that in LiTaO3, which is in agreement with the present LCAO based Mulliken's population analysis.

Nonlinear collision shifts of the 0-0 hyperfine transition due to van der Waals molecule formation.

We consider the origin of nonlinear collision shifts for the 0-0 hyperfine transition in alkali/noble-gas systems due to van der Waals molecule formation. Developing a semi-empirical model, we describe the shift as arising from three fundamental interactions: (1) a fractional change in the alkali's valence electron density at the alkali nucleus, η, which affects the hyperfine contact term; (2) a mixing of p-wavefunction character into the alkali ground state (characterized by the probability for p-state character appearing in the perturbed wavefunction ξ1 2), which gives rise to an electric quadrupole term in the ground-state hyperfine splitting; and (3) an interaction of the alkali's valence electron with the magnetic field produced by molecular rotation, characterized by a magnetic field strength BvdW. In addition to these molecular parameters, the model also depends on the formation rate of van der Waals molecules, kfP2, and the breakup rate of the molecules, kbP, where P is the noble-gas pressure. Fitting the model to the 85Rb/Xe and 87Rb/Xe experimental data of McGuyer and co-workers (and taking previously measured values for kf and BvdW), we find that η = 9 × 10-3, ξ1 2 = 5 × 10-3, and kb = 2.9×107s-1/Torr.

Hydrothermal synthesis and controlled growth of group-VIB W metal compound nanostructures from tungsten oxide to tungsten disulphide.

Two-dimensional lateral group-VIB transition metal dichalcogenides (TMDs) have attracted much attention in the fast evolving field of advanced photoelectric functional materials, but their controllable fabrication is challenging. Herein, an emerging synthetic route for sulfurization of tungsten oxide was developed. During the hydrothermal reaction, the optimization of the precursor selection and synthesis parameters led to the tunable properties of WO3-WSxOy-WS2 nanostructures. The vulcanization was thermodynamically favorably at low temperatures and in an environment with a sufficient S source, wherein WO3 was reduced by H atoms to WO3-x, and S atoms were preferentially adsorbed on O vacancies. The WSxOy nanostructures have a narrow band-gap attributed to the effect of S on the valence band top and electronic density of states by density functional theory. The photocurrent response and charge transfer properties of WSxOy were improved due to the charge transport between WS2 and WO3. Understanding the formation and transformation of WS2 nanostructures in solution contributes to the discovery of the important structure-efficiency relationship, which may be extended to other TMDs systems. Hence, extensive research efforts are still needed to develop safer and more efficient synthesis and modification methods to fully utilize the distinctive advantageous properties of TMDs in the photoelectric field.