Atomic Orbital Interactions Research Articles

Uncovering an Interfacial Band Resulting from Orbital Hybridization in Nickelate Heterostructures.

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO3 synthesized on a series of single-crystal substrates. Unlike nanofilms synthesized on other substrates, NdNiO3 on SrTiO3 (NNO/STO) gives rise to a unique band structure featuring an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by orbital hybridization between the Ti 3d orbitals of the STO substrate and the O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. These findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin films, thereby offering key insights into tuning their interfacial properties.

Symmetry-Shaped Singularities in High-Temperature Superconductor H3S.

The superconducting critical temperature of H3S ranks among the highest measured, at 203 K. This impressive value stems from a singularity in the electronic density-of-states, induced by a flat-band region that consists of saddle points. The peak sits right at the Fermi level, so that it gives rise to a giant electron-phonon coupling constant. In this work, we show how atomic orbital interactions and space group symmetry work in concert to shape the singularity. The body-centered cubic Brillouin Zone offers a unique 2D hypersurface in reciprocal space: fully connecting squares with two different high-symmetry points at the corners, Γ and H, and a third one in the center, N. Orbital mixing leads to the collapse of fully connected 1D saddle point lines around the square centers, due to a symmetry-enforced s-p energy inversion between Γ and H. The saddle-point states are invariably nonbonding, which explains the unconventionally weak response of the superconductor's critical temperature to pressure. Although H3S appears to be a unique case, the theory shows how it is possible to engineer flat bands and singularities in 3D lattices through symmetry considerations.

Identifying atomically thin isolated-band channels for intrinsic steep-slope transistors by high-throughput study

Developing low-power FETs holds significant importance in advancing logic circuits, especially as the feature size of MOSFETs approaches sub-10 nanometers. However, this has been restricted by the thermionic limitation of SS, which is limited to 60 mV per decade at room temperature. Herein, we proposed a strategy that utilizes 2D semiconductors with an isolated-band feature as channels to realize sub-thermionic SS in MOSFETs. Through high-throughput calculations, we established a guiding principle that combines the atomic structure and orbital interaction to identify their sub-thermionic transport potential. This guides us to screen 192 candidates from the 2D material database comprising 1608 systems. Additionally, the physical relationship between the sub-thermionic transport performances and electronic structures is further revealed, which enables us to predict 15 systems with promising device performances for low-power applications with supply voltage below 0.5 V. This work opens a new way for the low-power electronics based on 2D materials and would inspire extensive interests in the experimental exploration of intrinsic steep-slope MOSFETs.

The Mechanism of Ozone Oxidation of Coal and the Revelation of Coal Macromolecular Structure by Oxidation Products.

Ozone was injected into a coal-water suspension, and an HRTEM test was carried out on the separated oxidation products. The results show that from the perspective of visualization the macromolecular network structure of coal contains a large number of graphite-like structures. However, the chemical reaction mechanism between the coal surface and O3 is not clear, and the microscopic formation mechanism of oxygen-containing functional groups in carbon quantum dots has not been explained. As a result, the reaction process between O3 and methylene on the coal surface was studied by the DFT method. We found that OH• generated by O3 in water can oxidize two adjacent carbon atoms in methylene into double bonds (C=C), and finally, aldehydes and carboxylic acids were generated. By calculation of thermodynamic parameters ΔG and ΔH, it is found that all reactions are spontaneous exothermic processes. The above chemical reaction is based on the physical adsorption of OH• with Ar-(CH2)6-Ar and O3 with Ar-CH2-CH=CH-(CH2)3-Ar. The calculated adsorption energies of the two systems are -9.41 and -12.55 kcal/mol, respectively. Then, the charge transfer and atomic orbital interaction before and after adsorption are analyzed from the perspectives of Mulliken charge, density of states, deformation density, and total charge density. The results show that the electrostatic attraction is the main driving force of adsorption. The ether bond (C-O-C) in coal is finally oxidized to an ester group (RCOOR'), the hydroxyl group (CH2-CH-OH) on the aliphatic chain is oxidized to a carbonyl group (CH2-C=O), and the benzene with two OH• forms phenol hydroxyl and one molecule of water. Finally, the coal and the corresponding coal-based carbon quantum dots were investigated by infrared spectroscopy; the difference in functional groups before and after oxidation was clarified, and the result was in good agreement with the simulation.

Analysis of the adsorption characteristics of SF6 and its decomposition products in ZIF-67: based on GCMC and DFT

Given the superior performance of SF6 in arc extinguishing and its wide application in high voltage fields, the search for new adsorbent materials for SF6 and its main decomposition products holds significant importance in mitigating greenhouse gas potential and its implications for the environment and energy sectors. We chose ZIF-67, an organic framework with a high specific surface area and distinctive pore size structure, to address this important issue. Using the grand canonical Monte Carlo simulation approach, we investigated the adsorption of SF6 and its main decomposer gases by ZIF-67 at GPa. The interaction of ZIF-67 with SF6 and its main breakdown products was then examined at the level of atomic orbital interactions, with the adsorption energy and density of states estimated using density functional theory. The findings reveal that ZIF-67 has the best ability to capture H2S, with a saturation capacity of 3.2 mmol g−1 at room temperature. Its adsorption capacity for SOF2 and SO2F2 is about five to seven times higher than that of industrial adsorbents kdhF-03, and the working conditions are milder. The molecule radius and adsorption capacity are tightly correlated. An innovative method for the widespread recovery and treatment of SF6 and its byproducts is presented in this research. This paper aims to provide new insights and solutions to promote sustainable development in the power industry.

Treating Semiempirical Hamiltonians as Flexible Machine Learning Models Yields Accurate and Interpretable Results.

Quantum chemistry provides chemists with invaluable information, but the high computational cost limits the size and type of systems that can be studied. Machine learning (ML) has emerged as a means to dramatically lower the cost while maintaining high accuracy. However, ML models often sacrifice interpretability by using components such as the artificial neural networks of deep learning that function as black boxes. These components impart the flexibility needed to learn from large volumes of data but make it difficult to gain insight into the physical or chemical basis for the predictions. Here, we demonstrate that semiempirical quantum chemical (SEQC) models can learn from large volumes of data without sacrificing interpretability. The SEQC model is that of density-functional-based tight binding (DFTB) with fixed atomic orbital energies and interactions that are one-dimensional functions of the interatomic distance. This model is trained to ab initio data in a manner that is analogous to that used to train deep learning models. Using benchmarks that reflect the accuracy of the training data, we show that the resulting model maintains a physically reasonable functional form while achieving an accuracy, relative to coupled cluster energies with a complete basis set extrapolation (CCSD(T)*/CBS), that is comparable to that of density functional theory (DFT). This suggests that trained SEQC models can achieve a low computational cost and high accuracy without sacrificing interpretability. Use of a physically motivated model form also substantially reduces the amount of ab initio data needed to train the model compared to that required for deep learning models.

Atomic and Superatomic Orbital Interactions in In8FeNan Clusters

Atomic and Superatomic Orbital Interactions in In8FeNan Clusters

Study of structural and electronic properties of few-layer MoS2 film

Transition Metal Dichalcogenides (TMDs) such as MoS2 are important 2D materials due to their attractive electronic, optical and, catalytic properties. Among its various applications, the MoS2 based sensor development requires, preparation of thin film of MoS2 at a large scale. In this paper, we are reporting the synthesis of few-layers MoS2 films on SiO2/Si substrate using drop casting method. The MoS2 films are characterized using Optical Microscopy, Atomic Force Microscopy, Raman Spectroscopy, X- Ray Diffraction, Transmission Electron Microscopy and, Photoluminescence (PL) techniques. The Raman and AFM measurements indicate that the samples with 9–11 layers (≈ 8 nm). The XRD pattern reveals the hexagonal structure (2H) of MoS2 films. The observed (002) XRD peak at 2θ ≈ 14.4° corresponds to the interplanar spacing d (002) ≈ 6.14° A and lattice parameter c ≈ 12.28 °A. Hexagonal structure of grown film of MoS2 and interplanar spacing d (002) are reconfirmed by the FFT of the HRTEM image. The observed band structure using UV–Vis and PL results are compared with Density Functional Theory (DFT) and Density of States (DOS) calculations show the indirect band nature of few-layers MoS2 films. The calculated DOS and Partial Density of State (PDOS) plots show the formation of bands at different symmetry points due to atomic orbital interaction and the contribution of particular atoms and their orbitals. The obtained PL and UV–Vis spectra corresponding to the different energy levels are agreed with a calculated band gap at different symmetry points using DFT.

Phototribology: Control of Friction by Light.

In dry sliding, the coefficient of friction depends on the material pair and contact conditions. If the material and operating conditions remain unchanged, the coefficient of friction is constant. Obviously, we can tune friction by surface treatments, but it is a nonreversible process. Here, we report active control of friction forces on TiO2 thin films under UV light. It is reversible and stable and can be tuned/controlled with the light wavelength. The analysis of atomic force microscopy signals by wavelet spectrograms reveals different mechanisms acting in the darkness and under UV. Ab initio simulations on UV light-exposed TiO2 show a lower atomic orbital overlapping on the surface, which leads to a friction reduction of up to 60%. We suggest that photocontrol of friction is due to the modification of atomic orbital interactions from both surfaces at the sliding interface.

Band-Edge Orbital Engineering of Perovskite Semiconductors for Optoelectronic Applications.

Lead (Pb) halide perovskites have achieved great success in recent years because of their excellent optoelectronic properties, which is largely attributed to the lone-pair s orbital-derived antibonding states at the valence band edge. Guided by the key band-edge orbital character, a series of ns2-containing (i.e., Sn2+, Sb3+, and Bi3+) Pb-free perovskite alternatives have been explored as potential photovoltaic candidates. On the other hand, based on the band-edge orbital components (i.e., M2+ s and p/X- p orbitals), a series of strategies have been proposed to optimize their optoelectronic properties by modifying the atomic orbitals and orbital interactions. Therefore, understanding the band-edge electronic features from the recently reported halide perovskites is essential for future material design and device optimization. This Perspective first attempts to establish the band-edge orbital-property relationship using a chemically intuitive approach and then rationalizes their superior properties and explains the trends in electronic properties. We hope that this Perspective will provide atomic-level guidance and insights toward the rational design of perovskite semiconductors with outstanding optoelectronic properties.

Tuning the electronic structure of d0 perovskite oxides by combining distortive modes

Transition metal oxides in the ${d}^{0}$ perovskite class, defined broadly to include $\mathrm{W}{\mathrm{O}}_{3}$, have shown promise as light absorbers for photocatalytic applications. These compounds are highly tunable in their composition and atomic structure, and consequently, in their electronic structure and properties. Through the lens of atomic orbital interactions and density functional theory calculations, the present work explores how and why certain structural distortions tune the band gaps and band edges of $\mathrm{W}{\mathrm{O}}_{3}$ and ${d}^{0}$ perovskite oxides. It is determined that, because an individual distortive mode (e.g., polar distortion along or octahedral rotation around a cubic perovskite axis) changes the character of only some band-edge orbitals, combinations of distortive modes may tune band gaps much more significantly than the sum of individual modes. The implications of this tunability are discussed for $\mathrm{W}{\mathrm{O}}_{3}$ as a photocatalyst, and for ${d}^{0}$ perovskite oxides more generally.

Stone-Wales Defect and Vacancy-Assisted Enhanced Atomic Orbital Interactions Between Graphene and Ambient Gases: A First-Principles Insight.

Graphene has magnificent fundamental properties for its application in various fields. However, these fundamental properties have been observed to get perturbed by various agents like intrinsic defects and ambient gases. Degradation as well as p-type behavior of graphene under an ambient atmosphere are some of the properties that have not yet been explored extensively. In this work, interactions of different ambient gases, like N2, O2, Ar, CO2, and H2O, with pristine and defective graphene are studied using density functional theory (DFT) computations. It is observed that while the pristine graphene is chemically and physically inert with ambient gases, except for oxygen, its interaction with these ambient gases increases significantly in the presence of carbon vacancies and Stone–Wales (SW) defects. We report that Ar and N2 are apparently not inert with defective graphene, as they also influence its fundamental properties like band structure, mid gap (trap) states, and Fermi energy level. We have also found that while oxygen makes pristine graphene p-type, the phenomenon amplifies in the presence of SW defects. Besides, in the presence of carbon vacancies, N2, H2O, and CO2 also make the graphene monolayer p-type. Among ambient gases, oxygen is the real performance and reliability killer for graphene. Its reaction is seeded by a carbon vacancy, which initiates its degradation by local formation of graphene oxide.

Tuning of Structure Evolution and Electronic Properties through Palladium-Doped Boron Clusters: PdB16 as a Motif for Boron-Based Nanotubes.

Transition metal-doped electronic deficiency boron clusters have led to a vast variety of electronic bonding properties in chemistry and materials science. We have determined the ground state structures of PdBn0/- (n = 10-20) clusters by performing CALYPSO search and density functional theory (DFT) optimization. The identified lowest energy structures for both neutral and anionic Pd-doped boron clusters follow the structure evolution from two dimensional (2D) planar configurations to 3D distorted Pd-centered drum-like or tubular structures. Photoelectron spectra are simulated by time-dependent DFT theoretical calculations, which is a powerful method to validate our obtained ground-state structures. More interestingly, two "magic" number clusters, PdB12 and PdB16, are found with enhanced stability in the middle size regime studied. Subsequently, molecular orbital and adaptive natural density partitioning analyses reveal that the high stability of the PdB16 cluster originates from doubly σ π aromatic and bonding interactions of d-type atomic orbitals of the Pd atom with tubular B16 units. The tubular C8v PdB16 cluster, with robust relative stability, is an ideal embryo for forming finite and infinite nanotube nanomaterials.

Orbital graph convolutional neural network for material property prediction

Material representations that are compatible with machine learning models play a key role in developing models that exhibit high accuracy for property prediction. Atomic orbital interactions are one of the important factors that govern the properties of crystalline materials, from which the local chemical environments of atoms is inferred. Therefore, to develop robust machine learningmodels for material properties prediction, it is imperative to include features representing such chemical attributes. Here, we propose the Orbital Graph Convolutional Neural Network (OGCNN), a crystal graph convolutional neural network framework that includes atomic orbital interaction features that learns material properties in a robust way. In addition, we embedded an encoder-decoder network into the OGCNN enabling it to learn important features among basic atomic (elemental features), orbital-orbital interactions, and topological features. We examined the performance of this model on a broad range of crystalline material data to predict different properties. We benchmarked the performance of the OGCNN model with that of: 1) the crystal graph convolutional neural network (CGCNN), 2) other state-of-the-art descriptors for material representations including Many-body Tensor Representation (MBTR) and the Smooth Overlap of Atomic Positions (SOAP), and 3) other conventional regression machine learning algorithms where different crystal featurization methods have been used. We find that OGCNN significantly outperforms them. The OGCNN model with high predictive accuracy can be used to discover new materials among the immense phase and compound spaces of materials

High-Resolution Laser Spectroscopic Survey of the H3Σu--X3Σg- Electronic Transition of Si2.

Rotationally resolved spectra of the H3Σu--X3Σg- electronic transition bands of Si2 have been experimentally studied using laser-induced fluorescence in the 380-520 nm range. Si2 molecules are produced in a supersonically expanding planar plasma by discharging a silane/argon gas mixture. In total, 44 bands belonging to the H3Σu--X3Σg- electronic transition system of the most abundant isotopologue 28Si2 are experimentally recorded. With a spectral resolution of ∼0.04 cm-1, the triplet spin-splitting structures in individual rotational transition lines are fully resolved. Detailed analyses on the high-resolution spectra have yielded an accurate determination of spectroscopic constants for both X3Σg- and H3Σu- states. The spin-spin interaction constants for the two triplet states are found to be comparable (λ ≈1.5 cm-1), which may originate from the 3p atomic orbital interaction in the triplet Si2 molecule. The measured isotopologue spectra of 29Si28Si and 30Si28Si indicate that the H3Σu--X3Σg- transition system of 29S28S and 30S28S can be reasonably reproduced by the isotope mass-scaling rule. Spectroscopic parameters, including the Franck-Condon factors, the Einstein coefficients, and the oscillator strengths, are also determined from the experimental results and the Rydberg-Klein-Rees (RKR) calculations. The agreement between the experimentally measured and calculated dispersed fluorescence spectra indicates that the RKR calculations with the molecular constants determined in this work can accurately reproduce the diatomic potentials of both states. These molecular data provide a benchmark in high-level theoretical studies on Si2 and likely other small silicon clusters.

Chalcogen-Assisted Enhanced Atomic Orbital Interaction at TMD–Metal Interface and Sulfur Passivation for Overall Performance Boost of 2-D TMD FETs

Metal-semiconductor interface is a bottleneck for efficient transport of charge carriers through Transition Metal Dichalcogenide (TMD) based field-effect transistors (FETs). Injection of charge carriers across such interfaces is mostly limited by Schottky barrier at the contacts which must be reduced to achieve highly efficient contacts for carrier injection into the channel. Here we introduce a universal approach involving dry chemistry to enhance atomic orbital interaction between various TMDs (MoS2, WS2, MoSe2 and WSe2) & metal contacts has been experimentally demonstrated. Quantum chemistry between TMDs, Chalcogens and metals has been explored using detailed atomistic (DFT & NEGF) simulations, which is then verified using Raman, PL and XPS investigations. Atomistic investigations revealed lower contact resistance due to enhanced orbital interaction and unique physics of charge sharing between constituent atoms in TMDs with introduced Chalcogen atoms which is subsequently validated through experiments. Besides contact engineering, which lowered contact resistance by 72, 86, 1.8, 13 times in MoS2, WS2, MoSe2 and WSe2 respectively, a novel approach to cure / passivate dangling bonds present at the 2D TMD channel surface has been demonstrated. While the contact engineering improved the ON-state performance (ION, gm, mobility and RON) of 2D TMD FETs by orders of magnitude, Chalcogen based channel passivation was found to improve gate control (IOFF, SS, & VTH) significantly. This resulted in an overall performance boost. The engineered TMD FETs were shown to have performance on par with best reported till date.

General rules of the sub-band gaps in group-IV (Si, Ge, and Sn)-doped I-III-VI2-type chalcopyrite compounds for intermediate band solar cell: A first-principles study

In this work, we have investigated Si, Ge and Sn doped at III-site(Ga or Al) in CuGaSe2, CuAlSe2, AgGaSe2, and AgAlSe2 as the candidates for intermediate band solar cell (IBSC), and demonstrated that the absolute energy levels of the intermediate band from a given group IV dopant in various Se-based chalcopyrite hosts do not show remarkable changes. This is resulted from the fact that the intermediate band originates from the same antibonding state of IV-s and Se-p states. The intermediate bands sequence of Ge∗ < Sn∗ < Si∗ from the different dopants in the same chalcopyrite host is explained by a simple model based on the atomic orbital energy and bond interaction. Furthermore, Sn-doped CuAlSe2 with the suitable main-gap and sub-gaps has been selected out as a potential candidate for IBSC, and alloying with isovalent cations to adjust to proper sub-band gaps has been demonstrated in Ge-doped (Ag,Cu)AlSe2 and Ag(Ga,Al)Se2.

Density functional theory study of small Ag cluster adsorbed on graphyne

Based on the density functional theory study, we investigated the adsorption behavior of small Agn nanoclusters (n = 1 to 4) on γ-graphyne including the adsorption configurations with the minimum total energy, the charge transfer and charge density. The electronic properties including the band structure and density of states (DOS) were also discussed. The results indicated that Ag2 cluster had the minimum adsorption energy and charge transfer which might result in difficult adsorption process. Except for Ag2, all the introduction of Ag cluster exhibited n-type doping. For different Ag cluster, the interactions of atomic orbitals between Ag and C atom also varied. Our results can have certain guidance meaning for future study of the physical and chemical properties of modified graphyne or other monolayer materials.

Iron L-Edge Absorption Spectroscopy of Iron Pentacarbonyl and Ferrocene in the Gas Phase.

Fe L-edge X-ray absorption spectra of gas-phase iron pentacarbonyl and ferrocene measured in total-ion yield mode are reported. Comparison to previously published spectra of free iron atoms and gaseous iron chloride demonstrates how the interplay of local atomic multiplet effects and orbital interactions in the metal-ligand bonds varies for the different systems. We find changes in the degree of metal-ligand covalency to be reflected in the measured 2p absorption onset. Orbital- or state-specific fragmentation is furthermore investigated in iron pentacarbonyl and ferrocene by analyzing the partial-ion-yield spectra at the Fe L-edge. Strong dependence of the yields of different fragments is observed in ferrocene in contrast to iron pentacarbonyl. This difference is attributed to the different degrees to which the 2p core hole is screened in the two systems and to which charge is rearranged in the Auger final states. We provide experimental benchmark spectra for new ab initio approaches for calculating metal L-edge absorption spectra of metal complexes.

Chemically Driven Enhancement of Oxygen Reduction Electrocatalysis in Supported Perovskite Oxides.

Perovskite oxides have the capacity to efficiently catalyze the oxygen reduction reaction (ORR), which is of fundamental importance for electrochemical energy conversion. While the perovskite catalysts have been generally utilized with a support, the role of the supports, regarded as inert toward the ORR, has been emphasized mostly in terms of the thermal stability of the catalyst system and as an ancillary transport channel for oxygen ions during the ORR. We demonstrate a novel approach to improving the catalytic activity of perovskite oxides for solid oxide fuel cells by controlling the oxygen-ion conducting oxide supports. Catalytic activities of (La0.8Sr0.2)0.95MnO3 perovskite thin-film placed on different oxide supports are characterized by electrochemical impedance spectroscopy and X-ray absorption spectroscopy. These analyses confirm that the strong atomic orbital interactions between the support and the perovskite catalyst enhance the surface exchange kinetics by ∼2.4 times, in turn, improving the overall ORR activity.