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Energy functionals which depend explicitly on orbital densities, rather than on the total charge density, appear when applying self-interaction corrections to density-functional theory; this is, e.g., the case for Perdew-Zunger and Koopmans-compliant functionals. In these formulations the total energy is not invariant under unitary rotations of the orbitals, and local, orbital-dependent potentials emerge. We argue that this is not a shortcoming, and that instead these potentials can provide, in a functional form, a simplified quasiparticle approximation to the spectral potential, i.e., the local, frequency-dependent contraction of the many-body self-energy that is sufficient to describe exactly the spectral function. As such, orbital-density-dependent functionals have the flexibility to accurately describe both total energies and quasiparticle excitations in the electronic-structure problem. In addition, and at variance with the Kohn-Sham case, orbital-dependent potentials do not require nonanalytic derivative discontinuities. We present numerical solutions based on the frequency-dependent Sham-Schliiter equation to support this view, and examine some of the existing functionals in this perspective, highlighting the very close agreement between exact and approximate orbital-dependent potentials. [ABSTRACT FROM AUTHOR]

Fully conjugated donor–acceptor block copolymers are established as model systems to elucidate fundamental mechanisms of photocurrent generation in organic photovoltaics. Using analysis of steady‐state photoluminescence quenching, exciton dissociation to a charge transfer state within individual block copolymer chains is quantified. By making a small adjustment to the conjugated backbone, the electronic properties are altered enough to disrupt charge transfer almost entirely. Strong intermolecular coupling of the electron donor is introduced by synthesizing block copolymer nanoparticles. Transient absorption spectroscopy is used to monitor charge generation in block copolymer isolated chains and nanoparticles. While efficient charge transfer is observed in isolated chains, there is no indication of complete charge separation. In the nanoparticles, long‐lived polarons are observed as early as ≈15 ns. Thus, aggregation of electron donors can facilitate efficient charge generation. Conjugated block copolymers are established as model systems to examine fundamental photophysics in organic donor–acceptor materials. Intramolecular charge transfer within isolated block copolymer chains is quantified. Block copolymer nanoparticles are synthesized to examine the effect of polymer donor aggregation on charge generation. While charge transfer is observed in isolated chains, charge‐separated states are observed only in block copolymer nanoparticles. [ABSTRACT FROM AUTHOR]

The environmental impact of amino acids on the release of SeO 4 2− immobilized into hydrotalcite (Mg 2 Al-LDH) which belongs to the layered double hydroxides (LDHs) family was investigated by experimental study and the observed layer structure of hydrotalcite was verified through density-functional theory (DFT) calculations. Glycine, l -cysteine, and l -aspartic acid, which have smaller molecular sizes, can release SeO 4 2− largely due to intercalation, unstabilization of Mg 2 Al-LDH and simple dissolution, while l -tryptophan and l -phenylalanine caused limited SeO 4 2− release due to their larger sizes and aromaticity. XRD patterns for the solid residues after intercalation of amino acids revealed that the layer distance of Mg 2 Al-LDH was partially expanded. The main peaks and shoulder features corresponding to d 003 diffraction were well explained by DFT simulations using glycine as a model: the layer spacing of the main peak is responsible for the remaining SeO 4 2− and singly stacked glycine molecule and the layer spacing of the shoulder peak was well explained by doubly stacked glycine molecules. Hydrogen bonds between amino acids and hydroxyl ions in the metallic layers of Mg 2 Al-LDH were responsible for the stable configuration of the intercalated Mg 2 Al-LDH. This study indicates potential limitations to the stability of low-level radioactive wastes of 79Se in repositories which are affected by smaller molecules of amino acids released through degradation of organic matters in the pedosphere. [Display omitted] • Effect of amino acids on the mobility of selenate in LDH was explored. • Smaller sizes of amino acids promoted the release of selenate from LDH. • DFT predicted the interlayer spaces of LDH after intercalation of amino acids. • Singly stacked configuration of glycine was the most stable in LDH. • Cysteine suppressed the Mg dissolution from LDH. [ABSTRACT FROM AUTHOR]

[Display omitted] • O-doped hollow porous surface C 3 N 4 (OCN) was produced by a one-pot synthesis. • OCN has excellent photocatalytic CIP degradation under visible light irradiation. • There is less recombination of electron-hole pairs due to O doping in C 3 N 4. Pollutants degradation via visible-light driven photocatalysts have attracted interest as a potentially efficient and sustainable approach for wastewater treatment. In the present study, a series of oxygen-doped hollow porous surface graphitic carbon nitride (OCN) has been prepared by one-pot thermal polycondensation of melamine with different amounts of polyoxyethylene stearyl ether as the oxygen source and template. The prepared OCN samples were utilized for the photocatalytic ciprofloxacin (CIP) degradation, which is a pharmaceutical waste, under visible light irradiation. The highest degradation performance for CIP was obtained from the OCN sample with 1 mg polyoxyethylene stearyl, which was three times greater than that of pristine C 3 N 4. The superior degradation performance of the OCN samples were observed due to the improved light absorption, less recombination rate of photogenerated electron and hole, and enhanced electron transportation, which was proven through the PL, photocurrent density, and EIS results. Thus, the proposed one-pot synthesis of OCN provides an effective method in producing potential photocatalysts for the removal of organic pollutants, such as discarded pharmaceuticals, in wastewater. [ABSTRACT FROM AUTHOR]

• ZTL/Fe@MT20% has excellent efficiency for photocatalytic Cr(VI) reduction. • The effect of Fe impurity on MT was firstly studied using DFT calculation. • The mid-gap state of Fe in MT promote the carriers' separation of the composite. • The Z-scheme heterojunction strongly inhibits the recombination of carrier. Zn-Ti layered double hydroxide/montmorillonite (ZTL/MT) and Fe-doped ZTL/MT (ZTL/Fe@MT20%) were prepared as photocatalyst for Cr(VI) reduction. The ZTL/Fe@MT20% exhibited the highest photocatalytic activity, suggesting that a combination of ZTL and Fe-bearing MT could enhance photocatalytic activity by suppressing the recombination of photogenerated electron-hole pairs. On the basis of electronic-structure calculations, a photocatalytic mechanism for Cr(VI) reduction and the effect of Fe3+ on the structure of MT in ZTL/MT composites is proposed by density functional theory approach, whereby Fe impurities in MT generate a new mid-gap state that induce a Z-scheme heterojunction with ZTL, leading to reduced recombination of the photogenerated charge carriers in ZTL. These results establish that MT can not only act as a support material but also play an important role for photocatalytic reaction when Fe impurities are present in its structure. [ABSTRACT FROM AUTHOR]

• The immobilization mechanisms of I– and IO 3 – in ettringite are different. • IO 3 – is energetically favorable to be accommodated in ettringite. • The energy barrier is observed for I– accommodation in ettringite. • The structural water determines the ions immobilization in ettringite. Low-level radioactive wastes are commonly immobilized in cementitious materials, where cement-based material can incorporate radionuclides into their crystal structure. Specifically, ettringite (Ca 6 Al 2 (OH) 12 (SO 4) 3 ∙26H 2 O) is known to stabilize anionic species, which is appealing for waste streams with radioactive iodine (129I) that persists as iodide (I–) and iodate (IO 3 –) in the cementitious nuclear waste repository. However, the structural information and immobilization mechanisms of iodine species in ettringite remain unclear. The present results suggested minimal I– incorporation into ettringite (0.05 %), whereas IO 3 – exhibited a high affinity for ettringite via anion substitution for SO 4 2– (96 %). The combined iodine K-edge extended X-ray absorption fine structure (EXAFS) spectra and first-principles calculations using density functional theory (DFT) suggested that IO 3 – was stabilized in ettringite by hydrogen bonding and electrostatic forces. Substituting IO 3 – for SO 4 2– was energetically favorable by –0.41 eV, whereas unfavorable substitution energy of 4.21 eV was observed for I– substitution. Moreover, the bonding charge density analysis of the substituted IO 3 – and I– anions into the ettringite structure revealed the interaction between intercalated ions with the structural water molecules. These results provided valuable insight into the long-term stabilization of anionic iodine species and their migration in cementitious nuclear waste repository or alkaline environments. [ABSTRACT FROM AUTHOR]

The interaction between interfacial water and transition metal oxides is a primary enabling step for the oxygen evolution reaction (OER). RuO 2 is a prototypical OER electrocatalyst whose ability to activate interfacial water molecules is essential to its OER activity. We image the dissociation of surface water into OH* and O* on RuO 2 (110), where * denotes adsorbed species, using atomic force microscopy. Starting from the surface-bound water molecules, which form a one-dimensional network along the rows of Ru surface sites, increasing the oxidative potential strips hydrogen away and transforms the water molecules into OH* and O*. This oxidative step changes the pattern of the adsorbates from one- to two-dimensional. First-principles calculations with interfacial polarization, capacitive charging, and adsorbate interactions attribute this evolution to the cooperative dehydrogenation of adsorbed water and OH* on RuO 2 . We use these results to map the surface phase diagram of RuO 2 (110) and provide a quantitative interpretation of its cyclic voltammetry. Our result provides the visualization of the water dissociation on a conductive oxide surface, a critical step in the OER, and demonstrates that the water activation is a collective phenomenon at RuO 2 (110) electrodes.

Charge carrier doping usually reduces the resistance of a semiconductor or insulator, but was recently found to dramatically enhance the resistance in certain series of materials. This remarkable antidoping effect has been leveraged to realize synaptic memory trees in nanoscale hydrogenated perovskite nickelates, opening a new direction for neuromorphic computing. To understand these phenomena, we formulate a physical phase-field model of the antidoping effect based on its microscopic mechanism and simulate the voltage-driven resistance change in the prototypical system of hydrogenated perovskite nickelates. Remarkably, the simulations using this model, containing only one adjustable parameter whose magnitude is justified by first-principles calculations, quantitatively reproduce the experimentally observed treelike resistance states, which are shown unambiguously to arise from proton redistribution-induced local band gap enhancement and carrier blockage. Our work lays the foundation for modeling the antidoping phenomenon in strongly correlated materials at the mesoscale, which can provide guidance to the design of novel antidoping-physics-based devices.

We employ analytical transmission electron microscopy (TEM) to correlate the structural and chemical environment variations within a stacked epitaxial thin film of the high entropy oxide (HEO) Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 O (J14), with two layers grown at different substrate temperatures (500 and 200 °C) using pulsed laser deposition (PLD). Electron diffraction and atomically resolved STEM imaging reveal the difference in out-of-plane lattice parameters in the stacked thin film, which is further quantified on a larger scale using four-dimensional STEM (4D-STEM). In the layer deposited at a lower temperature, electron energy loss spectroscopy (EELS) mapping indicates drastic changes in the oxidation states and bonding environment for Co ions, and energy-dispersive X-ray spectroscopy (EDX) mapping detects more significant cation deficiency. Ab initio density functional theory (DFT) calculations validate that vacancies on the cation sublattice of J14 result in significant electronic and structural changes. The experimental and computational analyses indicate that low temperatures during film growth result in cation deficiency, an altered chemical environment, and reduced lattice parameters while maintaining a single phase. Our results demonstrate that the complex correlation of configurational entropy, kinetics, and thermodynamics can be utilized for accessing a range of metastable configurations in HEO materials without altering cation proportions, enabling further engineering of functional properties of HEO materials.

Dirac and Weyl semimetals are a central topic of contemporary condensed matter physics, and the discovery of new compounds with Dirac/Weyl electronic states is crucial to the advancement of topological materials and quantum technologies. Here we show a widely applicable strategy that uses high configuration entropy to engineer relativistic electronic states. We take the AMnSb 2 (A = Ba, Sr, Ca, Eu, and Yb) Dirac material family as an example and demonstrate that mixing of Ba, Sr, Ca, Eu and Yb at the A site generates the compound (Ba 0.38 Sr 0.14 Ca 0.16 Eu 0.16 Yb 0.16 )MnSb 2 (denoted as A 5 MnSb 2 ), giving access to a polar structure with a space group that is not present in any of the parent compounds. A 5 MnSb 2 is an entropy-stabilized phase that preserves its linear band dispersion despite considerable lattice disorder. Although both A 5 MnSb 2 and AMnSb 2 have quasi-two-dimensional crystal structures, the two-dimensional Dirac states in the pristine AMnSb 2 evolve into a highly anisotropic quasi-three-dimensional Dirac state triggered by local structure distortions in the high-entropy phase, which is revealed by Shubnikov-de Haas oscillations measurements., (© 2024. The Author(s).)

There is tremendous interest in employing collective excitations of the lattice, spin, charge, and orbitals to tune strongly correlated electronic phenomena. We report such an effect in a ruthenate, Ca 3 Ru 2 O 7 , where two phonons with strong electron-phonon coupling modulate the electronic pseudogap as well as mediate charge and spin density wave fluctuations. Combining temperature-dependent Raman spectroscopy with density functional theory reveals two phonons, B 2 P and B 2 M , that are strongly coupled to electrons and whose scattering intensities respectively dominate in the pseudogap versus the metallic phases. The B 2 P squeezes the octahedra along the out of plane c-axis, while the B 2 M elongates it, thus modulating the Ru 4d orbital splitting and the bandwidth of the in-plane electron hopping; Thus, B 2 P opens the pseudogap, while B 2 M closes it. Moreover, the B 2 phonons mediate incoherent charge and spin density wave fluctuations, as evidenced by changes in the background electronic Raman scattering that exhibit unique symmetry signatures. The polar order breaks inversion symmetry, enabling infrared activity of these phonons, paving the way for coherent light-driven control of electronic transport., (© 2023. Springer Nature Limited.)

Selenium (Se) radioactive wastes can be disposed through stabilization/solidification (S/S) based on the cementitious matrix on hydration products, where hydrocalumite (Ca 2 Al-LDH) is expected to play an important role in the retention of SeO 4 2- . Natural organic matters (NOMs) are known to be a risk to affect the transportation and mobility of undesirable chemical species in the pedosphere which receives the low level radioactive wastes (LLW). In the present work, five amino acids were selected as the simplified models of NOMs in the pedosphere to explore their effects on the stability of Ca 2 Al-LDH after immobilized SeO 4 2- under alkaline conditions. As the loading amount of amino acids on Ca 2 Al-LDH increasing, release of SeO 4 2- was enhanced in HGly, H 2 Asp, and H 2 Cys series, while no enhancement was observed in HPhe and HTrp series. Density functional theory (DFT) calculation predicted ion-exchange of amino acids and CO 3 2- with SeO 4 2- in a unit cell of LDH model. The intercalation of Asp 2- and CO 3 2- caused 003 peaks in XRD sharper and d 003 decreased from 8.15 Å to 7.70 Å which is assigned to Ca 2 Al-LDH(Asp, CO 3 ). In H 2 Cys series, the 003 peaks were kept broad and SeO 4 2- was still relatively maintained in LDH which was caused by the lower amounts of intercalated CO 3 2- in the presence of H 2 Cys. Amino acids in the interlayer of Ca 2 Al-LDH have several possible configurations, where the most stable one is prone to be in a horizontal direction through hydrogen bonds and Ca-O chemical bonds. This provides an insight on the stability of selenate immobilized in hydrocalumite, which can be produced in cement disposing in the pedosphere for a long term of burying. Not only carbonate but also small molecular organic matters like amino acids possibly give environmental impact on the mobility of low level anionic radionuclides in LDH., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Integration of semiconducting transition metal dichalcogenides (TMDs) into functional optoelectronic circuitries requires an understanding of the charge transfer across the interface between the TMD and the contacting material. Here, we use spatially resolved photocurrent microscopy to demonstrate electronic uniformity at the epitaxial graphene/molybdenum disulfide (EG/MoS 2 ) interface. A 10× larger photocurrent is extracted at the EG/MoS 2 interface when compared to the metal (Ti/Au)/MoS 2 interface. This is supported by semi-local density functional theory (DFT), which predicts the Schottky barrier at the EG/MoS 2 interface to be ∼2× lower than that at Ti/MoS 2 . We provide a direct visualization of a 2D material Schottky barrier through combination of angle-resolved photoemission spectroscopy with spatial resolution selected to be ∼300 nm (nano-ARPES) and DFT calculations. A bending of ∼500 meV over a length scale of ∼2-3 μm in the valence band maximum of MoS 2 is observed via nano-ARPES. We explicate a correlation between experimental demonstration and theoretical predictions of barriers at graphene/TMD interfaces. Spatially resolved photocurrent mapping allows for directly visualizing the uniformity of built-in electric fields at heterostructure interfaces, providing a guide for microscopic engineering of charge transport across heterointerfaces. This simple probe-based technique also speaks directly to the 2D synthesis community to elucidate electronic uniformity at domain boundaries alongside morphological uniformity over large areas.