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He-atom scattering is a well established and valuable tool for investigating surface structure. The correct interpretation of the experimental data requires an accurate description of the He-surface interaction potential. A quantum-mechanical treatment of the interaction potential is presented using the current dominant methodologies for computing ground state energies (Hartree-Fock, local and hybrid-exchange density functional theory) and also a novel post-Hartree-Fock ab initio technique for periodic systems (a local implementation of Mo\ller-Plesset perturbation theory at second order). The predicted adsorption well depth and long range behavior of the interaction are compared with that deduced from experimental data in order to assess the accuracy of the interaction potential. [ABSTRACT FROM AUTHOR]

Periodic hybrid-exchange density functional theory calculations are used to explore the first layer of water at model oxide surfaces, which is an important step for understanding the photocatalytic reactions involved in solar water splitting. By comparing the structure and properties of SnO2(110) and TiO2(110) surfaces in contact with water, the effects of structural and electronic differences on the water chemistry are examined. The dissociative adsorption mode at low coverage (1/7 ML) up to monolayer coverage (1 ML) on both SnO2 and TiO2(110) surfaces is analysed. To investigate further the intermolecular interactions between adjacent adsorbates, monolayer adsorption on each surface is explored in terms of binding energies and bond lengths. Analysis of the water adsorption geometry and energetics shows that the relative stability of water adsorption on SnO2(110) is governed largely by the strength of the chemisorption and hydrogen bonds at the surface of the adsorbate–substrate system. However on TiO2(110), a more complicated scenario of the first layer of water on its surface arises in which there is an interplay between chemisorption, hydrogen bonding and adsorbate-induced atomic displacements in the surface. Furthermore the projected density of states of each surface in contact with a mixture of adsorbed water molecules and adsorbed hydroxyls is presented and sheds some light on the nature of the crystalline chemical bonds as well as on why adsorbed water has often been reported to be unstable on rutile SnO2(110). [ABSTRACT FROM AUTHOR]

Hybrid-exchange density functional theory calculations are carried out to determine the effects of A-site doping on the electronic and magnetic properties of the manganite series La1-xCaxMnO3. This study focuses on the ground state of an ordered Ca occupancy in a periodic structure. It is shown that the hybrid-exchange functional, Becke three-parameter Lee-Yang-Parr (B3LYP), provides an accurate and consistent description of the electronic structure for LaMnO3, CaMnO3, and La0.75Ca0.25MnO3. We have quantified the relevant structural, magnetic, and electronic energy contributions to the stability of the doped compound. An insight into the exchange coupling mechanism for the low hole density region of the phase diagram, where a polaron (anti-Jahn-Teller) forms, is also provided. This study completes a microscopic description of the lightly doped insulator with an antiferromagnetic-to-ferromagnetic and metal-to-insulator transition. [ABSTRACT FROM AUTHOR]

LaMnO3 is an inexpensive alternative to precious metals (e.g. platinum) as a catalyst for the oxygen reduction reaction in alkaline fuel cells. In fact, recent studies have shown that among a range of non-noble metal catalysts, LaMnO3 provides the highest catalytic activity. Despite this, very little is known about LaMnO3 in the alkaline fuel cells environment, where the orthorhombic structure is most stable. In order to understand the reactivity of orthorhombic LaMnO3 we must first understand the surface structure. Hence, we have carried out calculations on its electrostatically stable low index surfaces using hybrid-exchange density functional theory, as implemented in CRYSTAL09. For each surface studied the calculated structure and formation energy is discussed. Among the surfaces studied the (100) surface was found to be the most stable with a formation energy of 0.98 J m−2. The surface energies are rationalised in terms of the cleavage of Jahn–Teller distorted Mn–O bonds, the compensation of undercoordination for ions in the terminating layer and relaxation effects. Finally, the equilibrium morphology of orthorhombic LaMnO3 crystals is predicted, allowing us to speculate about likely surface reaction sites. [ABSTRACT FROM AUTHOR]

Periodic hybrid-exchange density functional theory calculations are used to predict the structure of water on the rutile TiO2(110) surface (Θ ≤ 1 ML), which is an important first step towards understanding the photocatalytic processes that occur in solar water splitting. A detailed model describing the water-water and water-surface interactions is developed by exploring thoroughly the adsorption energetics. The possible adsorption mode--molecular, dissociative, or mixed--and the binding energy are studied as a function of coverage and arrangement, thus separation, of adsorbed species. These dependencies (coverage and arrangement) have a significant influence on the nature of the interactions involved in the H2O-TiO2 system. The importance of both direct intermolecular and surface-mediated interactions between surface species is emphasized. Finally, to gain insight into the photooxidation of adsorbed species at the surface, the electronic structure of the predicted adsorbate-substrate geometries is analyzed in terms of total and projected density of states. [ABSTRACT FROM AUTHOR]

Abstract: A model for investigating surface adsorption in the limit of low coverage within a periodic supercell formalism is described. The model facilitates the analysis of the contributions to the adsorption energy in terms of interaction, distortion and binding constants defined between nearest and next-nearest adsorbed molecules; both direct and surface-mediated effects are considered. As an example the adsorption of vinyl fluoride at the rutile TiO2(110) surface is studied. [Copyright &y& Elsevier]

Abstract: The adsorption of vinyl fluoride on the rutile TiO2(110) surface has been simulated, on the basis of a recently proposed experimental model, using hybrid-exchange density functional theory. Different surface coverages have been considered and the lateral interaction between adsorbed vinyl fluoride molecules has been quantified through a simple model of nearest and next nearest neighbouring molecules. The vibrational frequencies of the adsorbed molecule have been calculated and are found to be in excellent agreement with those observed providing support for the proposed adsorption model. The effect of the adsorption on the electronic structure of the molecule and the surface have been characterised by computing electrostatic potential maps and the local density of states. [Copyright &y& Elsevier]

The observation of photocatalytic water splitting on the surface of anatase TiO2 crystals has stimulated many investigations of the underlying processes. Nevertheless, a molecular-level understanding of the reaction is not available. This requires knowledge of the crystal facets present, the atomistic structure of the surfaces, and thus the reaction sites involved. In this paper we establish the atomistic structure of two surfaces, vicinal to the low-energy (101) surface. We compute the relative stability and electronic properties of the (514) and (516) surfaces and compare these to the low-index (101), (001), and (100) surfaces. The (516) surface is remarkably stable, and is predicted to contribute significantly to the surface area of a crystallite in equilibrium. We simulate constant current scanning tunneling microscopy images and, by comparing with those measured, we conclude that a surface previously observed in a miscut single crystal is the (516) surface described here. The computed stability of this surface indicates that it will be present in TiO2 nanostructures and the relative positions of its band edges suggests that it will play a significant role in the water-TiO2 reactions in solar water splitting. [ABSTRACT FROM AUTHOR]

The phase stability of LaMnO3 with respect to its competing oxides is studied using hybrid-exchange density functional theory (DFT) as implemented in crystal09. The underpinning DFT total-energy calculations are embedded in a thermodynamic framework that takes optimal advantage of error cancellation within DFT. It has been found that by using the ab initio thermodynamic techniques described here, the standard Gibbs formation energies can be calculated to a significantly greater accuracy than was previously reported (a mean error of 1.6% with a maximum individual error of -3.0%). This is attributed to both the methodology for isolating the chemical potentials of the reference states, as well as the use of the Becke, three-parameter, Lee-Yang-Parr (B3LYP) functional to thoroughly investigate the ground-state energetics of the competing oxides. [ABSTRACT FROM AUTHOR]

In spintronics, a perennial goal has been the generation of organic spin-bearing semiconductor materials with magnetic ordering stable at room temperature. To this end, the class of transition metal phthalocyanines has shown much promise in fulfilling this ambition. In particular, alpha-phase cobalt (II) phthalocyanine (α-CoPc) exhibits strong antiferromagnetic exchange interactions producing a long range order up to ∼100 K. However, the underlying mechanism by which this magnetic interaction proceeds is not well understood. In this report, a simple mechanism has been proposed based on the Hubbard Hamiltonian, which elucidates the exchange coupling in α-CoPc. The mechanism provides stipulations for increasing the magnetic coupling, and this directs to a proposal that substitution of the central cobalt ion for rhodium will lead to a significant increase in coupling strength. The strength of this exchange interaction has been evaluated using broken symmetry hybrid exchange density functional theory and indicates that the novel rhodium (II) phthalocyanine system is indeed predicted to exhibit significantly stronger magnetic ordering. This study, therefore, identifies the coupling mechanism in α-CoPc as primarily attributable to kinetic exchange, explains its previously reported strong coupling relative to its first-row transition metal counterparts, and suggests that rhodium (II) phthalocyanine is likely to exhibit stable magnetic ordering at room temperature., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).)

Sprouts are increasingly present in the human diet, being tasty and healthy foods high in antioxidant compounds. Although there is a body of literature on the sprouting of many plant species, Camelina sativa (L.) Crantz has not yet been studied for this purpose. This study aimed to characterize the main bioactive compounds and antioxidant potential of seeds and sprouts of five different Camelina cultivars (ALBA, CO46, CCE43, JOELLE, and VERA). In particular, the contents of phenolic compounds (PCs), phenolic acids (PAs), and glucosinolates (GLSs) were investigated. PCs, PAs, GLSs, and the antioxidant activity of seeds differed among cultivars and were greatly increased by sprouting. A PCA analysis underlined both the effect of the cultivar (PC2) and the germination (PC1) on the nutritional properties of Camelina. The best nutritional properties of seeds were observed for ALBA and CCE43, while the best nutritional properties of sprouts were recorded for CCE43 and JOELLE, since the latter cultivar showed a greater enhancement in phytochemical content and antioxidant activity with sprouting. Finally, a UHPLC-UV procedure for the analysis of GLSs in Camelina was developed and validated. The performance criteria of the proposed method demonstrated that it is useful for the analysis of GLSs in Camelina., Competing Interests: The authors declare no conflict of interest.

A family of boron nitride (BN)-based photocatalysts for solar fuel syntheses have recently emerged. Studies have shown that oxygen doping, leading to boron oxynitride (BNO), can extend light absorption to the visible range. However, the fundamental question surrounding the origin of enhanced light harvesting and the role of specific chemical states of oxygen in BNO photochemistry remains unanswered. Here, using an integrated experimental and first-principles-based computational approach, we demonstrate that paramagnetic isolated OB 3 states are paramount to inducing prominent red-shifted light absorption. Conversely, we highlight the diamagnetic nature of O-B-O states, which are shown to cause undesired larger band gaps and impaired photochemistry. This study elucidates the importance of paramagnetism in BNO semiconductors and provides fundamental insight into its photophysics. The work herein paves the way for tailoring of its optoelectronic and photochemical properties for solar fuel synthesis., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Well designed and optimized epitaxial heterostructures lie at the foundation of materials development for photovoltaic, photocatalytic, and photoelectrochemistry applications. Heterostructure materials offer tunable control over charge separation and transport at the same time preventing recombination of photogenerated excitations at the interface. Thus, it is of paramount importance that a detailed understanding is developed as the basis for further optimization strategies and design. Oxides of copper are nontoxic, low cost, abundant materials with a straightforward and stable manufacturing process. However, in individual applications, they suffer from inefficient charge transport of photogenerated carriers. Hence, in this work, we investigate the role of the interface between epitaxially aligned CuO and Cu 2 O to explore the potential benefits of such an architecture for more efficient electron and hole transfer. The CuO/Cu 2 O heterojunction nature, stability, bonding mechanism, interface dipole, electronic structure, and band bending were rationalized using hybrid density functional theory calculations. New electronic states are identified at the interface itself, which are originating neither from lattice mismatch nor strained Cu-O bonds. They form as a result of a change in coordination environment of CuO surface Cu 2+ cations and an electron transfer across the interface Cu 1+ -O bond. The first process creates occupied defect-like electronic states above the valence band, while the second leaves hole states below the conduction band. These are constitutional to the interface and are highly likely to contribute to recombination effects competing with the improved charged separation from the suitable band bending and alignment and thus would limit the expected output photocurrent and photovoltage. Finally, a favorable effect of interstitial oxygen defects has been shown to allow for band gap tunability at the interface but only to the point of the integral geometrical contact limit of the heterostructure itself.

The electronic and spintronic properties of the monovacancies in freestanding and isotopically compressed graphene are investigated using hybrid exchange density functional perturbation theory. When the effects of electronic self-interaction are taken into account, an integer magnetic moment of 2 μ B is identified for a Jahn-Teller reconstructed V 1 (5-9) monovacancy in freestanding graphene. For graphene with stable ripples induced by a compressive strain of 5%, a bond reconstruction produces a V 1 (55-66) structure for the monovacancy, which is localized at the saddle points of the ripple. The sizeable local distortion induced by reconstruction modifies both the geometric and electronic properties of rippled graphene and quenches the magnetic moment of the vacancy due to the sp 3 hybridization of the central atom. The nonmagnetic V 1 (55-66) structure is found to be stable on rippled structures, with the formation energy ∼2.3 eV lower than that of the metastable distorted V 1 (5-9) structures localized at sites other than the saddle points. The electronic ground state of distorted V 1 (5-9) corresponds to a wide range of fractional magnetic moments (0.50-1.25 μ B ). The computed relative stabilities and the electronic and magnetic properties of the V 1 (5-9) structures are found to be closely related to their local distortions. This analysis of the fundamental properties of defective graphene under compression suggests a number of strategies for generating regular defect patterns with tuneable magnetic and electronic properties and may, therefore, be used as a novel technique to achieve more precise control of graphene electronic structure for various application scenarios such as transistors, strain sensors, and directed chemisorption., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)