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Spin state is often regarded as the crucial valve to release the reactivity of energy‐related catalysts, yet it is also challenging to precisely manipulate, especially for the active center ions occupied at the specific geometric sites. Herein, a π–π type orbital coupling of 3d (Co)‐2p (O)‐4f (Ce) was employed to regulate the spin state of octahedral cobalt sites (CoOh) in the composite of Co3O4/CeO2. More specifically, the equivalent high‐spin ratio of CoOh can reach to 54.7 % via tuning the CeO2 content, thereby triggering the average eg filling (1.094) close to the theoretical optimum value. The corresponding catalyst exhibits a superior water oxidation performance with an overpotential of 251 mV at 10 mA cm−2, rivaling most cobalt‐based oxides state‐of‐the‐art. The π–π type coupling corroborated by the matched energy levels between Ce t1u/t2u‐O and CoOh t2g‐O π type bond in the calculated crystal orbital Hamilton population and partial density of states profiles, stimulates a π‐donation between O 2p and π‐symmetric Ce 4fyz2 orbital, consequently facilitating the electrons hopping from t2g to eg orbital of CoOh. This work offers an in‐depth insight into understanding the 4f and 3d orbital coupling for spin state optimization in composite oxides. [ABSTRACT FROM AUTHOR]

Iron‐based single‐atom catalysts (Fe─N─C) exhibit excellent oxygen reduction activity but struggle with bifunctional performance due to their poor oxygen evolution activity. Although the Fe spin state is found to be closely associated with enhanced bifunctional activity, controllably regulating the Fe spin state remains a challenge. Here, the controllable regulation of Fe spin state is directly achieved through competitive coordination between chlorine and pyridine nitrogen in the axial direction of Fe─N4. The spin state of Fe is regulated from high spin to intermediate spin by the modulation of axial ligands from weak‐field ligand chlorine to strong‐field ligand pyridinic nitrogen, which leads to the enhanced bifunctional activity of N─FeN4 with a small potential gap (ΔE = 0.68 V). Theoretical calculations indicate that the spin state turning is accompanied by an enhanced binding strength between Fe sites and *OH leading to a significant decrease in the OER barrier. Moreover, N─FeN4 exhibits sufficient durability for oxygen reduction reaction (ORR) (over 50 h), oxygen evolution reaction (OER) (over 200 h), and the assembled zinc–air battery (over 1000 h). Here a novel approach is proposed for designing efficient catalysts based on spin state and profound insights into Fe─N─C spin state for bifunctional oxygen catalysis. [ABSTRACT FROM AUTHOR]

Due to structural complexity and limited understanding, precise chemical modification in atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts requires theoretical calculations to optimize electronic, geometric, and catalytic performance and experimental implementation of learned lessons to improve their catalytic performance towards oxygen reduction reaction (ORR). Herein, we conducted a density functional theory (DFT) investigation to understand the effect of the replacement of O-atoms in Fe–O 4 –C by N-atoms in the first coordination shell of Fe-site (constructing five models: Fe–O 4 –C, Fe–O 3 N–C, Fe–N 2 O 2 –C, Fe–ON 3 –C and Fe–N 4 –C) towards ORR. The geometric and electronic calculations of these models suggested that replacing all the O-atoms with N-atoms around the Fe-site would make it more conducive to the adsorption of ORR intermediates. Moreover, the Gibbs free energy calculations demonstrated that the Fe-site becomes the active centre for 2e− ORR, leading to the dominant generation of H 2 O 2 when Fe is coordinated with four O-atoms (Fe–O 4 –C). Whereas in compounds like Fe–N 2 O 2 –C, Fe–O 3 N–C, and Fe–N 4 –C, where the Fe-site displays 4e− ORR, form water is a preferred product if the O-atoms are replaced by N-atoms, as in Fe–N 2 O 2 –C, Fe–O 3 N–C, and Fe–N 4 –C. This study would provide a fundamental understanding of how atomically dispersed M-N-C catalysts' electrocatalytic activity is affected by changes in the coordination environment of metal sites. [Display omitted] • A theoretical approach was used to construct the models of Fe-NxOy-C-based electrocatalysts. • The models Fe–O 4 –C, Fe–NO 3 –C, M–N 2 O 2 –C, M–N 3 O–C, and M-N4-C, were completely investigated via DFT approaches. • The O 2 adsorption at the Fe–N 4 –C catalyst was the determining step during the associative pathway. • The M-N 4 -C catalytic moel displayed 4e- ORR, while the M-O 4 -C catalyst showed 2e- ORR. [ABSTRACT FROM AUTHOR]

Spin-state transitions are an important research topic in complex oxides with the diverse magnetic states involved. In particular, the low-spin to high-spin transition in LaCoO3 thin films has drawn a wide range of attention due to the emergent ferromagnetic state. Although various mechanisms (e.g., structural distortion, oxygen-vacancy formation, spin-state ordering) have been proposed, an understanding of what really underlies the emergent ferromagnetism remains elusive. Here, the ferromagnetism in LaCoO3 thin films is systematically modulated by varying the oxygen pressure during thin-film growth. Although the samples show dramatic different magnetization, their cobalt valence state and perovskite crystalline structure remain almost unchanged, ruling out the scenarios of both oxygen-vacancy and spin-ordering. This work provides compelling evidence that the tetragonal distortion due to the tensile strain significantly modifies the orbital occupancy, leading to a low-spin to high-spin transition with emergent ferromagnetism, while samples grown at reduced pressure demonstrate a pronounced lattice expansion due to cation-off-stoichiometry, which suppresses the tetragonal distortion and the consequent magnetization. This result not only provides important insight for the understanding of exotic ferromagnetism in LaCoO3 thin films, but also identifies a promising strategy to design electronic states in complex oxides through cation-stoichiometry engineering.

Abstract Using scanning tunneling microscopy and spectroscopy we demonstrate a revival of magnetism in 7-armchair nanoribbon by unpassivated atoms at the termini. Namely, a pair of intense Kondo resonances emerges at the peripheries of zigzag terminus revealing the many-body screening effects of local magnetic moments. Although Kondo resonance originates from a missing local orbital, it extends to a distance of 2.5 nm along the edge of the ribbon. The results are complemented by density functional theory calculations which suggest a possible coupling between Kondo states despite screening effects of substrate electrons. These findings indicate a possibility to restore intrinsic magnetic ordering in graphene nanoribbon without major structural modifications.

The article discusses the production and properties of two-dimensional atomic layers of transition metal dichalcogenides (TMDs), focusing on the optical properties of monolayers. It begins with an introduction to the discovery of graphene production methods and the subsequent interest in TMDs. The basic properties of TMD monolayers, their crystal structure, and Brillouin zone are detailed. The article explores the energy spectrum of electrons in different valleys and the effective Hamiltonian describing states in parallel spin bands. The discussion extends to the matrix elements of interband optical transitions, including single-, two-, and three-photon transitions. Equations are provided to calculate probabilities of optical transitions, incorporating factors such as polarization vector, frequency of light, and temperature of the sample. Theoretical analysis of constituent matrix elements for these transitions is outlined, emphasizing quantum mechanical aspects. The article contributes researching of the optical behavior of transition metal dichalcogenides (TMDs) monolayers, particularly in structures with complex compositions.

Using scanning tunneling microscopy and spectroscopy we demonstrate a revival of magnetism in 7-armchair nanoribbon by unpassivated atoms at the termini. Namely, a pair of intense Kondo resonances emerges at the peripheries of zigzag terminus revealing the many-body screening effects of local magnetic moments. Although Kondo resonance originates from a missing local orbital, it extends to a distance of 2.5 nm along the edge of the ribbon. The results are complemented by density functional theory calculations which suggest a possible coupling between Kondo states despite screening effects of substrate electrons. These findings indicate a possibility to restore intrinsic magnetic ordering in graphene nanoribbon without major structural modifications. [ABSTRACT FROM AUTHOR]

<>Two dimensional (2D) materials are used to manufacture the various gadgets. Their properties are therefore appealing. In the present work, we have studied the structural, electronic, and magnetic properties of 2D bilayer hexagonal-Boron Nitride (h-BN), single B vacancy defect on h-BN (B-hBN), single N vacancy defect on h-BN (N-hBN), water adsorption; on B-hBN (w-B-hBN) and on N-hBN (w-N-hBN), materials by spin-polarized density functional theory (DFT) methods employing Quantum ESPRESSO (QE) computational tools. The structural stability of the h-BN, B-hBN, N-hBN, w-B-hBN, & w-N-hBN materials has been investigated by determining their minimum ground state energy and binding energy, and found that they are stable materials. The pristine h-BN bilayer supercell structure is also found to be more compact than other defective configurations. By analyzing the band structures and density of states (DoS) plots of these materials, we have examined their electronic properties, and found that pristine h-BN has a broad bandgap, whereas B-hBN, N-hBN, w-B-hBN, & w-N-hBN exhibit semiconducting nature. The DoS and partial density of states (PDoS) computations of the considered materials are used to study their magnetic properties. It is found that pristine h-BN is a non-magnetic, and B-hBN, N-hBN, w-B-hBN & w-N-BN are magnetic materials. Therefore, vacancy defects on pristine h-BN, and water adsorption on vacancy defected h-BN materials cause it to change from non-magnetic to magnetic. They could find use in the domain of device applications.

The dispersion of metal atoms across the surface of 1D and 2D carbon systems is the most accessible method for controlling their properties, which are attractive for various applications in electronics, energy, and catalysis. This work explores the features of the interaction between titanium atoms and the surface of carbon nanotubes using ab initio computer-simulation methods based on density functional theory. The investigation focuses on the peculiarities induced by the presence of various types of structural defects on these surfaces. To conduct the study, we select (7, 7) and (11, 0) nanotubes with similar diameters (≈1 nm) but with different types of conductivity: metallic and semiconductor type, respectively. Three types of defects are investigated: single vacancy, double vacancy, and topological defect. Two possible orientations of each type of defect relative to the axis of the tube are considered. The primarily used basis set is the atomic orbital basis (SIESTA package), and the plane-wave basis set (VASP package) is also employed in some test calculations. Computational experiments show that the binding energy of Ti atoms to a defect-free nanotube is always lower than that to defective nanotubes, regardless of the approximation used for the exchange-correlation functional (LDA or GGA). The binding energy values predicted in the LDA approximation are noticeably higher than those in the GGA approximation (up to ~15% for the (7, 7) tube and up to ~50% for the (11, 0) tube). Strongest binding occurs when titanium is adsorbed on a nanotube with a single vacancy; the resulting configuration can be considered as a defect where one carbon atom is replaced by a titanium atom. [ABSTRACT FROM AUTHOR]

This study explores the optical properties of monolayers from transition metal dichalcogenides (TMDs), materials that have gained attention post-graphene discovery for their unique electronic and optical characteristics. We analyze the crystal structure, Brillouin zones, and electronic band structures of TMD monolayers, laying the foundation to understand their diverse optical phenomena. Special emphasis is placed on the energy spectrum across valleys and the use of an effective Hamiltonian for parallel spin bands. We investigate interband optical transitions, including single-, two-, and three-photon processes, developing equations to calculate transition probabilities that take into account polarization, light frequency, and temperature. Our theoretical analysis, rooted in quantum mechanics, sheds light on the matrix elements that dictate these transitions, underscoring the impact of complex compositions on the optical behavior of TMD monolayers. This work not only advances our understanding of TMD optical properties but also highlights their potential for optoelectronic applications, marking a significant contribution to the field of semiconductor physics. [ABSTRACT FROM AUTHOR]

We report the single crystal XRD and MicroED structure, magnetic susceptibility, and EPR data of a series of CaMn3IV O4 and YMn3IV O4 complexes as structural and spectroscopic models of the cuboidal subunit of the oxygen-evolving complex (OEC). The effect of changes in heterometal identity, cluster geometry, and bridging oxo protonation on the spin-state structure was investigated. In contrast to previous computational models, we show that the spin ground state of CaMn3IV O4 complexes and variants with protonated oxo moieties need not be S=9/2. Desymmetrization of the pseudo-C3 -symmetric Ca(Y)Mn3IV O4 core leads to a lower S=5/2 spin ground state. The magnitude of the magnetic exchange coupling is attenuated upon oxo protonation, and an S=3/2 spin ground state is observed in CaMn3IV O3 (OH). Our studies complement the observation that the interconversion between the low-spin and high-spin forms of the S2 state is pH-dependent, suggesting that the (de)protonation of bridging or terminal oxygen atoms in the OEC may be connected to spin-state changes.

Spin‐state transitions are an important research topic in complex oxides with the diverse magnetic states involved. In particular, the low‐spin to high‐spin transition in LaCoO3 thin films has drawn a wide range of attention due to the emergent ferromagnetic state. Although various mechanisms (e.g., structural distortion, oxygen‐vacancy formation, spin‐state ordering) have been proposed, an understanding of what really underlies the emergent ferromagnetism remains elusive. Here, the ferromagnetism in LaCoO3 thin films is systematically modulated by varying the oxygen pressure during thin‐film growth. Although the samples show dramatic different magnetization, their cobalt valence state and perovskite crystalline structure remain almost unchanged, ruling out the scenarios of both oxygen‐vacancy and spin‐ordering. This work provides compelling evidence that the tetragonal distortion due to the tensile strain significantly modifies the orbital occupancy, leading to a low‐spin to high‐spin transition with emergent ferromagnetism, while samples grown at reduced pressure demonstrate a pronounced lattice expansion due to cation‐off‐stoichiometry, which suppresses the tetragonal distortion and the consequent magnetization. This result not only provides important insight for the understanding of exotic ferromagnetism in LaCoO3 thin films, but also identifies a promising strategy to design electronic states in complex oxides through cation‐stoichiometry engineering. [ABSTRACT FROM AUTHOR]

Molecular level understanding of 3d-transition metal interaction with water molecules in various electronic states is of fundamental significance in chemistry and biology. This study systematically presents the propensity of 3d-transition metals in their variable electronic and spin states towards solvation and splitting water molecules. The topological analysis affirmed that neutral and mono-cationic complexes are prone to be partially covalent in nature from moving low to high spin states; however, coordinate bonding is observed in di- and tri-cationic ion–water complexes. Potential energy surface analysis showed a profound influence of electronic states of 3d-transition metals on the relative feasibility of bond scission and solvation competing pathways. The early neutral, high spin mono-cationic, and di-cationic transition metals prefer solvation over splitting the water molecule. Similarly, mid- and late-transition metal ions in the first two electronic states, irrespective of the spin state, show higher preferences towards solvation. In contrast, neutral and tri-cationic ions tend to form either insertion complexes, hydroxides, or hydrides over the ion–water complexes, suggesting a preference to split the water molecule. Thus, tuning the electronic and micro-environment will help in the design of transition metals catalysts for water splitting. [ABSTRACT FROM AUTHOR]

Rational design and engineering of high‐performance, low‐cost electrocatalysts represents a critical first step in the development of sustainable energy technologies. While single‐atom catalysts (SACs) have emerged as viable candidates, recent research has shown that the structure and activity can be further manipulated and enhanced by the incorporation of a second metal center in the close proximity, forming a binuclear configuration. Such dual‐atom catalysts (DACs) are recognized as feasible choices to break the limitations of SACs due to the synergetic effects between the bimetallic atoms and their special structures. Herein, the recent advances of DAC electrocatalysis for a range of important reactions, focusing on their synthesis, characterization, and performance, are summarized. The review is concluded with a perspective highlighting the challenges and future research directions. [ABSTRACT FROM AUTHOR]

Abstract Spin‐state transitions are an important research topic in complex oxides with the diverse magnetic states involved. In particular, the low‐spin to high‐spin transition in LaCoO3 thin films has drawn a wide range of attention due to the emergent ferromagnetic state. Although various mechanisms (e.g., structural distortion, oxygen‐vacancy formation, spin‐state ordering) have been proposed, an understanding of what really underlies the emergent ferromagnetism remains elusive. Here, the ferromagnetism in LaCoO3 thin films is systematically modulated by varying the oxygen pressure during thin‐film growth. Although the samples show dramatic different magnetization, their cobalt valence state and perovskite crystalline structure remain almost unchanged, ruling out the scenarios of both oxygen‐vacancy and spin‐ordering. This work provides compelling evidence that the tetragonal distortion due to the tensile strain significantly modifies the orbital occupancy, leading to a low‐spin to high‐spin transition with emergent ferromagnetism, while samples grown at reduced pressure demonstrate a pronounced lattice expansion due to cation‐off‐stoichiometry, which suppresses the tetragonal distortion and the consequent magnetization. This result not only provides important insight for the understanding of exotic ferromagnetism in LaCoO3 thin films, but also identifies a promising strategy to design electronic states in complex oxides through cation‐stoichiometry engineering.

Metasurfaces are a class of planar optical components that are engineered to manipulate electromagnetic waves, including their spin states in terms of circular polarizations. For example, the Pancharatnam–Berry (PB) phase has been exploited in metasurfaces for various spin functionalities, but these spin functionalities, exhibit conjugate relations for spin states. Recent advances combining the PB phase and propagation phase have implemented completely independent spin functionalities for spin states. However, the spin functionalities are fixed once the metasurfaces are designed. Here, this work proposes and demonstrates that the spin functionalities designed from the PB phase and propagation phase can be further extended by simply rotating the elements in a metasurface. This extension is based on a relationship between phase profiles of spin states that are acquired before and after the rotation. Proof‐of‐concept demonstrations are performed for the extended spin functionalities, including the conversion from spin angular momentum to orbital angular momentum, and spin‐dependent holograms. This extension may find use in relevant applications such as polarized display and dual‐polarized holography. [ABSTRACT FROM AUTHOR]

The solution of the Dirac equation with the Coulomb potential is used to analyze bound electron states in a hydrogen atom. The analysis is based on the fact that such states are characterized by a set of quantum numbers which describe definite values of the complete set of physical quantities that can be determined simultaneously. This set includes the energy, square of the total angular momentum, one of its component and a spinor invariant. The latter, spinor invariant gives two-valued quantum number which determines the sign of its eigenvalue. In addition to the known Dirac and Johnson–Lippman invariant, there exists a new one. Operators of these three spinor invariants do not commute between themselves which results in the degeneracy of the energy levels with respect to the two-valued quantum number. Three different systems of the eigenbispinor corresponding to the three spinor invariants are obtained and the generalized solution with free parameters is calculated. Variation of the free parameters transforms one particular solution into any other. It is shown that the electron probability densities and spin polarizations in an electron cloud depend essentially on the invariant set, demonstrating physical difference of the states corresponding to different spinor invariants. [ABSTRACT FROM AUTHOR]

The Co(salen) ([LCo(II)]) mediated hydrofunctionalization of alkenes is a highly significant method for forming enantioselective products. In this work, we conducted comprehensive computational investigations to gain insights of the reaction mechanism. The orbital analysis and intrinsic bond orbital analysis (IBO) were utilized to unravel the flow of electrons during the progress of the reaction. We explored various spin state surfaces to understand the possible pathways for the reaction. Initially, [LCo(II)] reacts with an oxidant tertbutyl peroxybenzoate, yielding [LCo(III)OC(O)Ph] and [LCo(III)OtBu]. Subsequently, [LCo(III)OC(O)Ph] reacts with silane to form cobalt hydride ([LCo(III)H]), with the triplet spin state surface being the preferred pathway, featuring an energy barrier of 14.2 kcal mol-1. IBO analysis across this step revealed that it involves the transfer of hydrogen as a hydride. Subsequently, the [LCo(III)H] complex in a triplet spin state undergoes a minimum energy crossing point (MECP) to transition into the singlet spin state, representing its most stable configuration. The [LCo(III)H] complex further reacts with styrene via hydrogen atom transfer on the singlet spin state surface, followed by oxidation and subsequent reaction with indole on the doublet spin surface to yield the hydrofunctionalized product. This work also explores potential enantioselective steps in the reaction., (© 2024 Wiley‐VCH GmbH.)

In this literature, we are concerned with the necessary condition for classicality and separability of the spin states by virtue of Cauthy tensors. The classicality and separability of the spin-j states are identified with the positive semidefiniteness of the 2j order associated tensor under tensor representation of quantum states. According to the properties of Bloch vector and trρ=1, we present necessary condition for classicality (separability) and entanglement of the spin-j states by virtue of Cauthy tensors with the positive generating vector c. This necessary condition not only perfectly maintains the physical properties of the quantum system, but also depends only on spin-j and the generating vector c. In addition, we show that Cauchy tensor method has a wider detection range and is easy to verify compared with the existing smallest tensor eigenvalue method.

We choose a typical three-site one-dimensional (1D) quantum chain system to deduce exact spin states and nonequilibrium spin transport properties analytically. The initial spin-up and spin-down electron charges on each site of the chain are calculated from the exactly derived spin ground state with the assumption of half-filling. Based on the Keldysh formalism, we describe the basic theoretical methods and derive some analytic formulas (differential spin conductance, spin transport current, electron charge distribution, etc.) for nonequilibrium spin transport of the 1D chain systems within the Hartree–Fock approximation when Coulomb electron interaction is present. The scattering processes including Coulomb repulsion between the spin-up and spin-down electrons, and spin–spin interactions due to spin degrees freedom are taken into account. We also report the numerical results of the nonequilibrium spin transport of the three-site 1D chain system in some special cases using the initial spin-up/down electron charges. [ABSTRACT FROM AUTHOR]

Heteroatom doped atomically dispersed Fe1‐NC catalysts have been found to show excellent activity toward oxygen reduction reaction (ORR). However, the origin of the enhanced activity is still controversial because the structure‐function relationship governing the enhancement remains elusive. Herein, sulfur(S)‐doped Fe1‐NC catalyst was obtained as a model, which displays a superior activity for ORR towards the traditional Fe‐NC materials. 57Fe Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy revealed that incorporation of S in the second coordination sphere of Fe1‐NC can induce the transition of spin polarization configuration. Operando 57Fe Mössbauer spectra definitively identified the low spin single‐Fe3+‐atom of C‐FeN4‐S moiety as the active site for ORR. Moreover, DFT calculations unveiled that lower spin state of the Fe center after the S doping promotes OH* desorption process. This work elucidates the underlying mechanisms towards S doping for enhancing ORR activity, and paves a way to investigate the function of broader heteroatom doped Fe1‐NC catalysts to offer a general guideline for spin‐state‐determined ORR. [ABSTRACT FROM AUTHOR]

We present herein the magnetic and Mössbauer investigation of a colorimetric chemical sensor with the chemical formula [Fe(H2btm)2(H2O)2]Cl2 (1) (H2btm = Di(1H-tetrazol-5-yl)methane). The spectra were recorded before and after sensing a series of toxic gases (MeOH, diethylenetriamine, hexylamine, 1,2-diaminocyclohexane, 3-picolylamine, pyridine and furfurylamine). Worth to note that the sensing process (color changes) proceeds at room temperature, does not require any pretreatment and can be detected as well by the naked eyes. 57Fe Mössbauer spectroscopy not only allows to identify the nature of spin states involved in our Fe(II) sensor but also to evaluate quantitatively the respective spin state population, i.e. high spin and low-spin states. [ABSTRACT FROM AUTHOR]

The electronic and geometric structures of the water‐oxidizing complex of photosystem II in the steps of the catalytic cycle that precede dioxygen evolution remain hotly debated. Recent structural and spectroscopic investigations support contradictory redox formulations for the active‐site Mn4CaOx cofactor in the final metastable S3 state. These range from the widely accepted MnIV4 oxo‐hydroxo model, which presumes that O−O bond formation occurs in the ultimate transient intermediate (S4) of the catalytic cycle, to a MnIII2MnIV2 peroxo model representative of the contrasting "early‐onset" O−O bond formation hypothesis. Density functional theory energetics of suggested S3 redox isomers are inconclusive because of extreme functional dependence. Here, we use the power of the domain‐based local pair natural orbital approach to coupled cluster theory, DLPNO‐CCSD(T), to present the first correlated wave function theory calculations of relative stabilities for distinct redox‐isomeric forms of the S3 state. Our results enabled us to evaluate conflicting models for the S3 state of the oxygen‐evolving complex (OEC) and to quantify the accuracy of lower‐level theoretical approaches. Our assessment of the relevance of distinct redox‐isomeric forms for the mechanism of biological water oxidation strongly disfavors the scenario of early‐onset O−O formation advanced by literal interpretations of certain crystallographic models. This work serves as a case study in the application of modern coupled cluster implementations to redox isomerism problems in oligonuclear transition metal systems. [ABSTRACT FROM AUTHOR]

We report the single crystal XRD and MicroED structure, magnetic susceptibility, and EPR data of a series of CaMn3IVO4 and YMn3IVO4 complexes as structural and spectroscopic models of the cuboidal subunit of the oxygen‐evolving complex (OEC). The effect of changes in heterometal identity, cluster geometry, and bridging oxo protonation on the spin‐state structure was investigated. In contrast to previous computational models, we show that the spin ground state of CaMn3IVO4 complexes and variants with protonated oxo moieties need not be S=9/2. Desymmetrization of the pseudo‐C3‐symmetric Ca(Y)Mn3IVO4 core leads to a lower S=5/2 spin ground state. The magnitude of the magnetic exchange coupling is attenuated upon oxo protonation, and an S=3/2 spin ground state is observed in CaMn3IVO3(OH). Our studies complement the observation that the interconversion between the low‐spin and high‐spin forms of the S2 state is pH‐dependent, suggesting that the (de)protonation of bridging or terminal oxygen atoms in the OEC may be connected to spin‐state changes. [ABSTRACT FROM AUTHOR]

Circular dichroism, as one of the exotic phenomena, derives from chirality biomolecules in nature, expressing differential absorption of spin angular momentum. The concept of dichroism has been migrated to the field of artificial materials and acquired adequate development. However, there is still a lack of a flexible strategy to tailor circular dichroism for providing another promising level to achieve spin‐selective multi‐dimensional manipulation of electromagnetic waves. In this work, a paradigm of reflective chiral metasurface is proposed to promote this aspect of exploration. By introducing loss resistors into the chiral meta‐atoms, the magnitude of differential absorption effect can be tailored by varying the corresponding resistance, leading to the variation of co‐polarization reflection amplitude. Combining with the Pancharatnam–Berry phases of chiral meta‐atom, both the reflective amplitude and phase are flexibly controlled in independent manners. Accordingly, the pattern of reflection fields can be theoretically shaped into arbitrary forms through Fourier transform in spatial domain. Here, metasurfaces for achieving rectangular‐shaped beam and complex‐amplitude hologram are demonstrated as two proofs‐of‐principle. Encouragingly, this effort provides an alternative approach for simultaneous control of amplitude and phase, which may pave a new route in the fields of beam‐forming technology and spin‐selective integrated systems. [ABSTRACT FROM AUTHOR]

[Display omitted] Photoelectrochemical (PEC) water splitting for solar energy conversion into chemical fuels has attracted intense research attention. The semiconductor hematite (α-Fe 2 O 3), with its earth abundance, chemical stability, and efficient light harvesting, stands out as a promising photoanode material. Unfortunately, its electron affinity is too deep for overall water splitting, requiring additional bias. Interface engineering has been used to reduce the onset potential of hematite photoelectrode. Here we focus instead on energy band engineering hematite by shrinking the crystal lattice, and the water-splitting onset potential can be decreased from 1.14 to 0.61 V vs. the reversible hydrogen electrode. It is the lowest record reported for a pristine hematite photoanode without surface modification. X-ray absorption spectroscopy and magnetic properties suggest the redistribution of 3 d electrons in the as-synthesized grey hematite electrode. Density function theory studies herein show that the smaller-lattice-constant hematite benefits from raised energy bands, which accounts for the reduced onset potential. [ABSTRACT FROM AUTHOR]

The Infrared (IR) and Raman spectra of various interstitial carbon defects in silicon are computed at the quantum mechanical level by using an all electron Gaussian type basis set, the hybrid B3LYP functional and the supercell approach, as implemented in the CRYSTAL code (Dovesi et al. J. Chem. Phys. 2020, 152, 204111). The list includes two 〈100〉 split interstitial IXY defects, namely ICC and ICSi, a couple of related defects that we indicate as IXIY, the so called CiCs0 in its A and B form, as well as SiCiSi and CsCiCs, in which the interstitial carbon atom is twofold coordinated. The second undergoes a large relaxation, and the final configuration is close to ICCCs. Geometries, relative stabilities, electronic, and vibrational properties are analysed. All these defects show characteristic features in their IR spectrum (above 730 cm−1), whereas the Raman spectrum is dominated, in most of the cases, by the pristine silicon peak at 530 cm−1, that hides the defect peaks. [ABSTRACT FROM AUTHOR]

Guiding electromagnetic waves carrying spin angular momentum is an important issue in both optical and microwave communities that thus has intrigued enormous interest in the past few decades. In particular, asymmetrical propagation is seriously considered as a possibility to push the development of encryption communication and electromagnetic circulators, which is a hot area but still a challenge. Circular dichroism, referring to differential absorption of distinct polarization states, provides an alternative scheme to achieve asymmetric propagation in a spin‐correlated way. Here, a paradigm of obtaining broadband asymmetric reflection to push the exploration in this aspect is proposed. With this aim, an N‐shaped resonator loaded with two lumped resistors is designed as a meta‐atom to reveal the amplitude flipping of nearly 0 and 1 for distinct polarization states. Combining with Pancharatnam–Berry phases, the arbitrary phase profile of a designated spin state can be achieved. As a proof‐of‐principle, a robust meta‐mirror is fabricated to acquire broadband electromagnetic focusing under the illumination of left‐handed circularly polarized (LHCP) wave. On the other hand, the reflection of right‐handed circularly polarized (RHCP) wave is substantially suppressed. Both numerical simulation and experimental measurement are carried out to demonstrate the feasibility of this system. [ABSTRACT FROM AUTHOR]

• The Fe spin state of Fe(II)Cl 2 (tpm) has been studied by experimental and theoretical investigation. • Theoretical investigation are performed on XAS at the Fe L 2,3 -edges and N K-edge. • The best agreement has been obtained for a low-spin, diamagnetic ground state. • The stability depends upon the ligands, the bulk solvent and the interaction of the vacant site. • Both tpm→Fe(II) σ bonding and a tpm⟵Fe(II) Charge Transfer characterize the Fe–tpm interaction. The Fe(II) spin state in the condensed phase of [Fe(II)Cl2(tpm)] (tpm = [tris(pyrazol-1-yl)methane]; 1) catalyst has been determined through a combined experimental and theoretical investigation of X-Ray Absorption Spectroscopy (XAS) at the FeL 2,3 -edges and NK-edge. Results indicated that in this phase a mixed singlet/triplet state is plausible. These results have been compared with the already know Fe singlet spin state of the same complex in water solution. A detailed analysis of the electronic structure and bonding mechanism of the catalyst showed that the preference for the low-spin diamagnetic ground state, strongly depends upon the ligands, the bulk solvent and the interaction of the complex's vacant site (the sixth) with a further ligand. Moreover, comparison of the electronic properties of the complex in condensed phase and water solution showed an increased Lewis acidity of the catalyst in solution phase, due to a decreasing of the LUMO energy of about 8 kcal/mol. These results gave an overall picture of the electronic behavior of the complex investigated, on going from condensed to water solution phase, explaining the preferred use of 1 as catalyst in homogeneous catalysis. The N Fe(II) interaction has been thoroughly investigated by means of DFT Kohn-Sham and EDA bond analysis applied to i) the isolated [Fe(II)Cl 2 (tpm)] and ii) the [Fe(II)Cl 2 (tpm)] interacting with water as a solvent within the Conductor-like Screening Mode (COSMO) framework. Results showed that both tpm→Fe(II) σ and tpm⟵Fe(II) π Charge Transfer (CT) interactions characterize the Fe(II)–tpm interaction. Moreover, the three tpm N atoms do not equally interact with the Fe(II) and one of them shares a suitable available iron-based d virtual orbital, to bind a further ligand in trans position. [ABSTRACT FROM AUTHOR]

Carbenes are challenging molecular species for quantum chemistry because of the energetic proximity of their singlet and triplet spin states and the sensitive dependence of spin-state energetics on the geometry of the carbene site. Here we use an extended set of aryl-carbenes to evaluate the performance of density functional theory (DFT) approximations as well as of wave function based perturbation theory approaches (orbital-optimised perturbation theory methods OO-MP2 and OO-SCS-MP2) against reference coupled cluster calculations with singles, doubles and perturbative triples conducted with the aid of the domain-based local pair natural orbitals approach, DLPNO-CCSD(T). In addition to the expected functional dependence, our results document a remarkable discordance in the performance of DFT methods in the sense that the functionals that yield the best geometries do not coincide with those that provide the best spin-state energetics. Analysis of the results allows us to propose a series of methods that are expected to perform reliably within certain confidence limits for the title systems. Additionally, methodological issues regarding the reference singlet–triplet gaps obtained by the DLPNO-CCSD(T) approach are discussed. [ABSTRACT FROM AUTHOR]

Extensive high‐level quantum‐chemical calculations reveal that the rod‐shaped molecule BeOBeC, which was recently generated in matrix experiments, exists in two nearly isoenergetic states, the 5Σ quintet (56) and the 3Σ triplet (36). Their IR features are hardly distinguishable at finite temperature. The major difference concerns the mode of spin coupling between the terminal beryllium and carbon atoms. Further, the ground‐state potential‐energy surface of the [2Be,C,O] system at 4 K is presented and differences between the photochemical and thermal behaviors are highlighted. Finally, a previously not considered, so far unknown C2v‐symmetric rhombus‐like four‐membered ring 3[Be(O)(C)Be] (35) is predicted to represent the global minimum on the potential‐energy surface. [ABSTRACT FROM AUTHOR]

The adsorption of the iron tetraphenylporphyrin (FeTPP) molecule in its deckchair conformation was investigated on Au(111), Ag(111) and Cu(111) surfaces by performing spin-polarized density functional theory (DFT) calculations taking into account both van der Waals (vdW) interaction and on-site Coulomb repulsion. The deckchair conformation of the molecule favours intermolecular π–π-type interactions in a less densely packed monolayer than the saddle conformation. The activation barrier between the two stable magnetic states (high spin, S = 2 and intermediate spin, S = 1) of the molecule in vacuum disappears upon adsorption on the metal surfaces. The high-spin state of physisorbed FeTPP is stable on all adsorption sites. This result reveals that an external permanent element such as a STM tip or an additional molecule is needed to use FeTPP or similar molecules as model system for molecular spin switches.

We investigated the Kondo effect of cobalt(II)-5-15-bis(4'-bromophenyl)-10,20-bis(4'-iodophenyl)porphyrin (CoTPPBr 2 I 2 ) molecules on Au(111) with low-temperature scanning tunneling microscopy under ultrahigh vacuum conditions. The molecules exhibit four adsorption configurations at the top and bridge sites of the surface with different molecular orientations. The Kondo resonance shows extraordinary sensitivity to the adsorption configuration. By switching the molecule between different configurations, the Kondo temperature is varied over a wide range from ≈8 up to ≈250 K. Density functional theory calculations reveal that changes of the adsorption configuration lead to distinct variations of the hybridization between the molecule and the surface. Furthermore, we show that surface reconstruction plays a significant role for the molecular Kondo effect.

We present results of soft X-ray absorption spectroscopy studies of EuBaCo 2 O 5.5 powders subjected to mechanical impact (milling in a ball mill). We show that in the near-surface region (5–10 nm) of particles of the powder, EuBaCo 2 O 5.5 decomposes into Co 3 O 4 , BaCO 3 , and EuCoO 3. A knowledge of the low-spin state of Co3+ ions in EuCoO 3 and Co 3 O 4 and possibilities of surface-sensitive soft X-ray absorption spectroscopy have allowed to determine the composition of the EuBaCo 2 O 5.5 sample subjected to mechanical impact near its surface, which is inaccessible to standard X-ray phase analysis. Unlabelled Image • EuBaCo 2 O 5.5 powders are subjected to mechanical impact in a ball mill. • The samples are studied by surface-sensitive soft X-ray absorption spectroscopy. • Products of reaction in the near-surface area are Co 3 O 4 , BaCO 3 , and EuCoO 3. • Co3+ ions in EuCoO 3 are in a low-spin state. [ABSTRACT FROM AUTHOR]

We discuss the possibility to formulate the dynamics of spin states described by the Schr¨odinger equation for pure states and the von Neumann equation (as well as the GKSL equation) for mixed states in the form of quantum kinetic equations for probability distributions. We review an approach to the spin-state description by means of the probability distributions of dichotomic random variables. [ABSTRACT FROM AUTHOR]