First-principles Theory Research Articles

Thermal Rates and High-Temperature Tunneling from Surface Reaction Dynamics and First-Principles.

Studying dynamics of the dissociative adsorption and recombinative desorption of hydrogen on copper surfaces has shaped our atomic-scale understanding of surface chemistry, yet experimentally determining the thermal rates for these processes, which dictate the outcome of catalytic reactions, has been impossible so far. In this work, we determine the thermal rate constants for dissociative adsorption and recombinative desorption of hydrogen on Cu(111) between 200 and 1000 K using data from reaction dynamics experiments. Contrary to current understanding, our findings demonstrate the predominant role of quantum tunneling, even at temperatures as high as 400 K. We also provide precise values for the reaction barrier (0.619 ± 0.020 eV) and adsorption energy (0.348 ± 0.026 eV) for H2 on Cu(111). Remarkably, the thermal rate constants are in excellent agreement with a first-principles quantum rate theory based on a new implementation of ring polymer molecular dynamics for reactions on surfaces, paving the way to discovering better catalysts using reliable and efficient computational methods.

Observation of Aromatic B13(CO)n+ (n = 1-7) as Boron Carbonyl Analogs of Benzene.

CO as a typical σ-donor is one of the most important ligands in chemistry, while planar B13+ is experimentally known as the most prominent magic-number boron cluster analogous to benzene. Joint gas-phase mass spectroscopy, collision-induced dissociation, and first-principles theory investigations performed herein indicate that B13+ reacts with CO successively under ambient conditions to form a series of boron carbonyl complexes B13(CO)n+ up to n = 7, presenting the largest boron carbonyl complexes observed to date with a quasi-planar B13+ core at the center coordinated by nCO ligands around it. Extensive theoretical analyses unveil both the chemisorption pathways and bonding patterns of these aromatic B13(CO)n+ monocations which, with three delocalized π bonds well-retained over the slightly wrinkled B13+ moiety, all prove to be boron carbonyl analogs of benzene tentatively named as boron carbonyl aromatics (BCAs). Their π-isovalent B12(CO)n (n = 1-6) complexes with a quasi-planar B12 coordination center are predicted to be stable neutral BCAs.

Enhanced adsorption and sensing properties of Ptn(n=1,3)-doped SnS2 monolayers for warfare toxic gases: A DFT Study

Toxic gases have been extensively employed in warfare, spanning from the deployment of irritant tear gas to fatal nerve gas. These chemical armaments have caused significant damage and casualties in times of conflict. This study explores the adsorption properties and sensing mechanisms of three chemical warfare agents(chlorine Cl2, phosgene COCl2, chloropicrin CCl3NO2) on both pristine SnS2 and doped SnS2 using density functional theory (DFT). The results highlight the superior adsorption energy, charge transfer efficiency, and band structure of doped Ptn/SnS2 (n=1,3) compared to pristine SnS2. Pt/SnS2 exhibits exceptional adsorption capabilities for all three war gases. Under specific conditions, Pt3/SnS2(cluster) emerges as an ideal material for detecting Cl2 and CCl3NO2, while also serving as an effective adsorbent for COCl2 gas. This research serves as a valuable reference for sensor performance studies grounded in first-principles theory, showcasing the potential of doped Pt3/SnS2 as a viable sensor for warfare gases. The insights from this study contribute to the development of advanced poison gas sensors, facilitating improvements in poison gas detection and prevention capabilities.

Exploration of Zr-doped PtSe2 monolayer for sensing C2H2 and C2H4 in oil-immersed transformers of HVDC converter station: A first-principles investigation

Using the first-principles theory, this work purposes Zr-doped PtSe2 (Zr-PtSe2) monolayer as a potential sensing material upon two typical dissolved gases (C2H2 and C2H4), in order to evaluate the operation status of the oil-immersed transformers. Zr-doping on the pristine PtSe2 monolayer is firstly analyzed, yielding the formation energy of −3.12 eV. The Zr-PtSe2 monolayer conducts chemisorption upon C2H2 and C2H4 with the adsorption energy of −1.40 and −1.02 eV, respectively. The electronic property analysis of the gas adsorbed systems reveal the much higher sensing response upon C2H2 molecule, and the recovery property analysis uncovers the reusability for the purposed material. Moreover, the work function is also analyzed to explore the sensing potential of Zr-PtSe2 monolayer based on its change after gas adsorption. The findings pave the way to explore the PtSe2-based material as gas sensors, providing informative guidance for gas sensing material exploration in the electrical engineering.

Insights of the Multimode Orientation-Dependent Initial Oxidation of Aluminum by First-Principles Theory Calculations.

A fundamental understanding of the oxidation mechanisms of aluminum (Al) alloys is of great importance for its applications in corrosion, catalysis, sensors, etc. In this work, we systematically investigated the first-stage oxidation behaviors of three low-index Al facets with O coverage up to two monolayers (ML) by using density-functional theory (DFT). The large negative adsorption energies indicated favorable oxidation on all three facets. However, distinctive structural and electronic changes induced by the adsorption of oxygen have led to different oxidation modes. More specifically, the oxidation process proceeded by "intercalating" into the subsurface region along the (111) plane out of the (110) facet with spontaneous O ingress into (110) far below one ML, as revealed by the electron density distribution, whereas the oxide ad-layer grew in a "layer-by-layer" mode on Al(111) and (001) facets. Moreover, various Al-O complexes with different atomic coordination numbers (CN), configurations, and sizes may be indicators of the tendency of an Al surface to be oxidized. Besides, the oxide phases formed on (111)/(001) and (110) assembled the Al-O bond distribution within α-Al2O3 and γ-Al2O3, respectively.

Development of new amine-functionalized metal-organic framework for enhanced triboelectrification using first-principle theory of nanogenerator

TENGs have gained significant attention due to their ability to convert mechanical energy into electricity. Advancements in materials like metal-organic frameworks (MOFs) and device architecture have led the improvements in performance. We used a first-principle theory nanogenerator to design and investigate the novel without and with amino-functionalized Zn-MOF (NH2-Zn-MOF) for the triboelectric properties. The amino functionalization possesses unconventional electrostatic functions with the change in the surface potential, work function and capacitance. V-shaped amine-functionalized Zn-MOF TENG device achieved a maximum peak-to-peak voltage of 624 V along with a maximum power density of 244 mW/m2. The amine functionalization results in a 2.5-fold increment in output performance than the non-functionalized device. The harvested energy is utilized for capacitor charging and powering low-powered electronics. Furthermore, the amino-functionalized MOF-TENG device proves as a promising smart sports sensor in detection and monitoring.

Micro-mechanism study of charge transfer at heterojunction interface based on first-principles theory: MoS2/SnO2 as the prototype

Gas sensors made of semiconductor heterojunctions have excellent gas-sensitive properties. However, sufficient theoretical evidence is still needed to prove that heterojunction improve gas sensitivity of a single-material. A typical case is studied here: MoS2/SnO2 heterojunction absorption of NO2 is investigated by first-principles calculations, to explore the enhancing-mechanism. Interestingly, it is found that electron transfer not only occurs between the material surface of the heterojunction and gas, but also involves the substrate atoms transferring electrons to the gas molecules through the surface atoms. This finding fills the response mechanism of heterojunction gas sensors and provides a theoretical basis for experiments.

First-Principles Investigation on Ru-Doped Janus WSSe Monolayer for Adsorption of Dissolved Gases in Transformer Oil: A Novel Sensing Candidate Exploration.

Using first-principles theory, this work purposes Ru-doped Janus WSSe (Ru-WSSe) monolayer as a potential gas sensor for detection of three typical gas species (CO, C2H2, and C2H4), in order to evaluate the operation status of the oil-immersed transformers. The Ru-doping behavior on the WSSe surface is analyzed, giving rise to the preferred doping site by the replacement of a Se atom with the formation energy of 0.01 eV. The gas adsorption of three gas species onto the Ru-WSSe monolayer is conducted, and chemisorption is identified for all three gas systems with the adsorption energy following the order: CO (-2.22 eV) > C2H2 (-2.01 eV) > C2H4 (-1.70 eV). Also, the modulated electronic properties and the frontier molecular orbital are investigated to uncover the sensing mechanism of Ru-WSSe monolayer upon three typical gases. Results reveal that the sensing responses of the Ru-WSSe monolayer, based on the variation of energy gap, to CO, C2H2, and C2H4 molecules are calculated to be 1.67 × 106, 2.10 × 105, and 9.61 × 103, respectively. Finally, the impact of the existence of O2 molecule for gas adsorption and sensing is also analyzed to uncover the potential of Ru-WSSe monolayer for practical application in the air atmosphere. The obtained high electrical responses manifest strong potential as a resistive sensor for detection of three gases. The findings hold practical implications for the development of novel gas sensing materials based on Janus WSSe monolayer. We anticipate that our results will inspire further research in this domain, particularly for applications in electrical engineering where the reliable detection of fault gases is paramount for maintaining the integrity and safety of power systems.

Spatio-temporal breather dynamics in microcomb soliton crystals

Solitons, the distinct balance between nonlinearity and dispersion, provide a route toward ultrafast electromagnetic pulse shaping, high-harmonic generation, real-time image processing, and RF photonic communications. Here we uniquely explore and observe the spatio-temporal breather dynamics of optical soliton crystals in frequency microcombs, examining spatial breathers, chaos transitions, and dynamical deterministic switching – in nonlinear measurements and theory. To understand the breather solitons, we describe their dynamical routes and two example transitional maps of the ensemble spatial breathers, with and without chaos initiation. We elucidate the physical mechanisms of the breather dynamics in the soliton crystal microcombs, in the interaction plane limit cycles and in the domain-wall understanding with parity symmetry breaking from third-order dispersion. We present maps of the accessible nonlinear regions, the breather frequency dependences on third-order dispersion and avoided-mode crossing strengths, and the transition between the collective breather spatio-temporal states. Our range of measurements matches well with our first-principles theory and nonlinear modeling. To image these soliton ensembles and their breathers, we further constructed panoramic temporal imaging for simultaneous fast- and slow-axis two-dimensional mapping of the breathers. In the phase-differential sampling, we present two-dimensional evolution maps of soliton crystal breathers, including with defects, in both stable breathers and breathers with drift. Our fundamental studies contribute to the understanding of nonlinear dynamics in soliton crystal complexes, their spatio-temporal dependences, and their stability-existence zones.

Highly efficient SnO2-Carbon nanosphere heterojunctions decorated with Ag for detecting isopropanol at low operating temperatures

The design of a sensing material for detecting isopropanol gas with low operating temperature is extremely important for miniaturization and wearability of gas sensors. Herein, a novel gas sensor based on SnO2-Carbon nanosphere heterojunctions decorated with Ag nanoparticles (SCA) was fabricated and its gas sensing performance was evaluated and compared systematically. The measurement results indicated that the sensing performance was influenced by the ratio of Sn/C and the length of Ag plating, and the SCA sensor provided the best response. For 100 ppm isopropanol at 100 °C, the SCA sensor exhibited a response value of 50.51, a response time of 7 s and a recovery time of 60 s. The enhanced sensing performance and reduced operating temperature of the SCA could be attributed to the synergistic effect of the SnO2-Carbon nanosphere heterojunctions and the significant catalytic performance of the decorated Ag nanoparticles. In addition, the density functional theory calculation method based on the first-principles theory was used to study the adsorption performance and electronic behavior, as well asthe influence of Ag decoration on SnO2 for isopropanol detection. The calculated results were consistent with the experimental results.

Two-Orders-of-Magnitude Enhancement of SERS Activity via a Simple Surface Engineering of Quasi-Metal Single-Crystal Frameworks.

Beyond noble metals and semiconductors, quasi-metals have recently been shown to be noteworthy substrates for surface enhanced Raman spectroscopy, and their excellent quasi-metal surface-enhanced Raman spectroscopy (SERS) sensing has demonstrated a wider range of application scenarios. However, the underlying mechanism behind the enhanced Raman activity is still unclear. Here, we demonstrate that surface hydroxyls play a crucial role in the enhancement of the SERS activity of quasi-metal nanostructures. As a demonstration material, quasi-metallic MoO2 single-crystal frameworks rich in surface hydroxyls have been shown to have 100 times higher SERS activity than MoO2 single-crystal frameworks without hydroxyl functionalization, with a Raman enhancement factor of up to 7.6 × 107. Experimental and first-principles density-functional theory calculation results show that the enhanced Raman activity can be attributed to an effective interfacial charge transfer within the MoO2/OH/molecule system.

Density functional theory study of physisorption of ionic liquid pairs on hydroxylated and oxygen terminated α-SiO2 (001) surfaces

In this work, we investigate the ion pair tetramethylphosphonium cation, [P1,1,1,1]+, and bis(oxalato)borate anion, [BOB]−, as a model system for the study of ionic liquids interacting with both hydroxylated and oxygen terminated α-SiO2 (001) surfaces, using first-principles electronic structure theory. We use a single ionic pair and clusters of ion pairs, in order to have exclusively neutral supercell slab models. We use dispersion-corrected density functional theory (DFT) to ascertain that both the strong physical binding between the ions, dominated by ionic binding, and the weaker physical binding of ions to the different surfaces are correctly described. We have found that the binding of ion pairs is stronger to the hydroxylated α-SiO2 (001) surface compared to the oxygen terminated surface, which is attributed to the formation of H-binding with the oxygen atom(s) of the [BOB]− anion. Through rotation of ionic pair(s), we estimate the surface-ions energy barrier for translational movement and, thus, the strength of H-binding of the ions. At the surface of hydroxylated α-SiO2 (001), we have studied how water molecules form a network of H-binding with the OH groups of the surface and the [BOB]− anion, which offers an explanation for the reduction in the friction of ionic liquids on the inclusion of water. We suggest modeling protocols for simulation of ion pairs on surfaces, which can open up the possibility to use DFT to aid in designing and understanding the physicochemical mechanism of interactions of ionic materials (including ionic liquids) in various technological applications.

PyArc: A python package for computing absorption and radiative coefficients from first principles

Light absorption and radiative recombination are two critical processes in optoelectronic materials that characterize the energy conversion efficiency. The absorption and radiative coefficients are thus key properties for device optimization and design. Here, we develop a python package named pyArc that allows rigorous computation of absorption and radiative coefficients from first principles. By integrating several interpolation strategies to augment k-point sampling in reciprocal space, our code is accurate yet highly efficient. In addition to evaluation of the coefficients, our code is capable of intuitive analysis of carrier distribution, facilitating a deeper understanding of the microscopic mechanisms underlying the radiative coefficients. Utilizing GaAs as a prototypical example, we demonstrate how to employ our package to compute absorption and radiative coefficients and to investigate the key features in the electronic structure that give rise to these coefficients. Program SummaryProgram title: PyArcCPC Library link to program files:https://doi.org/10.17632/5x9g9bvhcv.1Licensing provisions: MIT licenseProgramming language: Python 3Nature of problem: Light absorption and radiative recombination processes in semiconductors critically impact the energy conversion efficiency of optoelectronic devices. Developing a method to calculate coefficients of the two processes based on first-principles theory is essential, which not only can help to obtain the key properties of those semiconductor materials and guide the device design, but also can unveil the underlying microscopic mechanisms.Solution method: PyArc, written in the Python language, implements first-principles methodologies for the computation of absorption and radiative coefficients of semiconductors based on Fermi's golden rule. This package takes the electronic eigenvalues and dipole matrix elements of a material computed from first-principles codes such as VASP as input. Dense k-point sampling for the Brillouin zone is achieved through efficient interpolation schemes implemented in our code to acquire well converged results. The functionality of cross-sectional visualization of carrier distribution in our code provides intuitive insights into the fundamental mechanism beneath the charge-carrier radiative recombination process.

Prediction of Halogenated MXenes as Electrode Materials for Halide-Ion Batteries.

Exploring and developing new rechargeable halide-ion batteries plays an important role in the advancement and growth of the ion battery family. Here, we systematically explored the feasibility of single-layer MXenes and their hydrogenated derivatives as electrode materials for halide-ion batteries via first-principles theory. The calculated results indicate that halide ions (T ions) can be stably and efficiently adsorbed on the surfaces of M2X and M2XH2, with theoretical specific capacities ranging from 227 to 497 mAh g-1. The diffusion barriers of the T ion on MXenes are from 0.55 to 0.10 eV, comparable to those of the Li ion in graphite and LiCoO2. The electronegativity of halide anions displays significant impacts on their discharge voltage plateaus on M2X, with the highest voltage up to 5.60 V for the F ion. As a comparison, the hydrogenation of M2XH2 with less surface activity raises a 2-3 V voltage reduction. All MXene-based full cells of TxTi2C|TyTi2CH2 (where x = 0-2 and y = 2-0) and TxTi2N|TyTi2NH2 (where x = 0-2 and y = 2-0) demonstrated high full battery specific energies for F-, Cl-, and Br-ion batteries, up to 462 Wh kg-1. These results demonstrate the potential of new halide-ion battery designs, paving the way for future research and innovation in battery technology.

First-principles insights into the structural, mechanical, electronic, optical, and thermophysical properties of XSrBr3 (X = Na, Ga, and Tl) perovskites: Implications for optoelectronic applications

Non-toxic halide perovskite compounds possess critical inherent and improved features for use in optoelectronic devices. The present work summarizes the physical properties of cubic halide perovskites XSrBr3 (X = Na, Ga, and Tl) based on first-principles theory. The structural, electrical, optical, mechanical, and thermophysical properties of these compounds are studied to assess their potential utility in optoelectronics field. GGA-PBE and GGA-PBEsol functionals were utilized to determine the lattice properties, cell volumes, and formation energies of the compounds. The negative formation energies support the compounds' structural stability. The compounds' bandgaps were computed using the GGA-PBE and Hybrid-HSE06 functionals. Each of the three compounds has a wide indirect bandgap. Optoelectronic devices such as UV detectors, solar panel antireflection coatings, OLED, QLED, and waveguides benefit from a greater static dielectric constant, broad absorption spectra, and low visible reflectance. The elastic stiffness constants Cij use the necessary conditions to demonstrate that the NaSrBr3, GaSrBr3, and TlSrBr3 perovskite structures are mechanically stable. The elastic modulus and other trustworthy properties imply that perovskites are mechanically ductile and soft. In conclusion, the investigation indicates the potential applications of these perovskite materials in photovoltaic and optoelectronic technologies.

Nonlinear change of ion-induced secondary electron emission in the κ-Al2O3 surface charging from first-principle modelling

Secondary electron emission (SEE) induced by the positive ion is an essential physical process to influence the dynamics of gas discharge which relies on the specific surface material. Surface charging has a significant impact on the material properties, thereby affecting the SEE in the plasma-surface interactions. However, it does not attract enough attention in the previous studies. In this paper, SEE dependent on the charged surface of specific materials is described with the computational method combining a density functional theory (DFT) model from the first-principle theory and the theory of Auger neutralization. The effect of κ-Al2O3 surface charge, as an example, on the ion-induced secondary electron emission coefficient (SEEC) is investigated by analyzing the defect energy level and band structure on the charged surface. Simulation results indicate that, with the surface charge from negative to positive, the SEEC of a part of low ionization energy ions (such as E i = 12.6 eV) increases first and then decreases, exhibiting a nonlinear changing trend. This is quite different from the monotonic decreasing tendency observed in the previous model which simplifies the electronic structure. This irregular increase of the SEEC can be attributed to the lower escaped probability of orbital energy. The results further illustrate that the excessive charge could cause the bottom of the conduction band close to the valence band, thus leading to the decrease of the orbital energy occupied by the excited electrons. The nonlinear change of SEEC demonstrates a more realistic situation of how the electronic structure of material surface influences the SEE process. This work provides an accurate method of calculating SEEC from specific materials, which is urgent in widespread physical scenarios sensitive to surface materials, such as increasingly growing practical applications concerning plasma-surface interactions.

Broad band modulation of two-dimensional Mo1-x W x S2 by variational compositions

Precisely tuning bandgap enables tailored design of materials, which is of crucial importance for optoelectronic devices. Towards this end, ternary Mo1-x W x S2 monolayers with continually variational transition metal compositions are synthesized by precisely control of the precursors and growth temperatures in the chemical vapor deposition process, and thus to manipulate the bandgap of the monolayers. Energy dispersive x-ray spectroscopy demonstrates that the composition of the ternary Mo1-x W x S2 monolayers can be effectively modulated by the precursors and synthesizing temperatures. Frequency and intensity of the Raman and photoluminescent peaks of the Mo1-x W x S2 monolayers are continually modulated by the variational Mo and W compositions. The maximum of 0.148 eV bandgap modulation is achieved by modulating the transition metal compositions, which is highly consistent to the calculated 0.158 eV by first-principles theory. Photodetectors based on the Mo1-x W x S2 monolayers are fabricated and U-shape of photoresponse characteristics are demonstrated as x change from 0 to 1 under the same measurement conditions. The estimated photocurrent, photoresponsivity and external quantum efficiency show that the minimum values appear at the composition of x = 0.5, while the maximum values appear at x = 1. The results illustrate an excellent level of control on the band structure of two-dimensional ternary Mo1-x W x S2 by precisely control of the transition metal compositions.

Spatial-temporal self-attention network based on bayesian optimization for light olefins yields prediction in methanol-to-olefins process

Methanol-to-olefins (MTO), as an alternative pathway for the synthesis of light olefins (ethylene and propylene), has gained extensive attention. Accurate prediction of light olefins yields can effectively facilitate process monitoring and optimization, as they are significant economic indexes and stable operation indicators of the industrial MTO process. However, the nonlinearity and dynamic interactions among process variables pose challenges for the prediction using traditional statistical methods. Additionally, physical-based methods relying on first-principle theory are always limited by an insufficient understanding of reaction mechanisms. In contrast, data-driven methods offer a viable solution for the prediction based solely on process data without requiring extensive process knowledge. Therefore, in this work, a data-driven approach that integrates spatial and temporal self-attention modules is proposed to capture complex interactions. Furthermore, Bayesian optimization is employed to determine the optimum hyperparameters and enhance the accuracy of the model. Studies on an actual MTO process demonstrate the superior prediction performance of the proposed model compared to baseline models. Specifically, 24 process variables are selected as the high-dimensional inputs, and yields of ethylene and propylene, as the low-dimensional outputs, are successfully predicted at various prediction horizons ranging from 2 to 8 h.

Understanding off-stoichiometry of Q-phase in Al-Cu-Mg-Si alloys

We perform first-principles density-functional theory (DFT) calculations to resolve the controversy of off-stoichiometry of Q-phase in Al-Cu-Mg-Si system. We compute the single and multiple defect energies (vacancy-vacancy, anti-site–vacancy, anti-site–anti-site) at 0 K and finite temperatures to understand the gap between DFT-predicted lowest energy structure and experimentally observed various stoichiometries of Q-phase. We find that i) the stoichiometry of Al4Cu2Mg8Si7 observed by Arnberg can be explained by the single anti-site defect of Al on Mg site, ii) the stoichiometry of Al5Cu2Mg8Si6 observed by Phragmen can be understood by the multiple anti-site defects of Al on Mg site and Al on Si site, iii) the physical size effect is important in determining the defect formation energetics under a similar chemistry (i.e., composition) of Q-phase. We believe that the proposed defect energetic information and mechanism will be useful to design Q-phase strengthened aluminum alloys based on Integrated Computational Materials Engineering (ICME).

First-principles study of layer-dependent band alignment and work function in MoS[formula omitted] nanoflakes

MoS2 is renowned for its intriguing electronic and optical properties, which exhibit variations dependent on the number of layers and the atomic arrangement within its layers. In this work, we employ first-principles theory calculations to systematically investigate how interlayer spacing and layer number impact the electronic properties of MoS2 nanoflakes. The primary focus of this work is to comprehend the layer-dependent behaviors of the band gap, work function, and band alignment of MoS2. Our findings reveal that the MoS2 band gap experiences a reduction as the number of layers increases, following a power-law relationship, while the work function rises with an increasing layer count. Moreover, both band gap and work function increase with the expansion of the interlayer spacing in MoS2 layers. This study suggests that the layer-dependent characteristics of band edges and work functions in few-layer MoS2 offer valuable opportunities for the manipulation of Schottky barriers, ultimately enhancing carrier injection efficiency.