Ab Initio Molecular Dynamics Calculations Research Articles

Promoting Cl2O Generation from the HOCl + HOCl Reaction on Aqueous/Frozen Air-Water Interfaces.

Hypochlorous acid (HOCl) is considered a temporary reservoir of dichlorine monoxide (Cl2O). Previous studies have suggested that Cl2O is difficult to generate from the reaction of HOCl + HOCl in the gas phase. Here, we demonstrate that Cl2O can be generated from the HOCl + HOCl reaction at aqueous/frozen air-water interfaces, which is confirmed by ab initio molecular dynamic calculations. Distinct from the one-step reaction in the gas phase, our results show that Cl2O generation from HOCl + HOCl on aqueous/frozen interfaces involves two elementary steps, namely, one HOCl deprotonation and one Cl-abstraction from the other HOCl. Specifically, the mechanisms of neutral/acidic catalysis from interfacial water/nitric acid and base catalysis from ammonia, methylamine and dimethylamine have been examined. For the former, HOCl deprotonation is the rate-limiting step, and the total k of Cl2O generation increases to 9.23 × 10-9-9.10 × 10-1 M-1 s-1 at the aqueous interface and 3.20 × 10-7-4.10 × 10-3 M-1 s-1 at the frozen interface, which is at least 23 and 25 orders of magnitude greater than that of gaseous k (3.31 × 10-32 M-1 s-1). For the latter, the rate-limiting step is changed to Cl-abstraction, whose total k dramatically increases to 1.40-8.97 × 107 M-1 s-1 at the aqueous interface and 7.12-9.99 × 106 M-1 s-1 at the frozen interface. Interestingly, the Cl2O production rates ranked in the order of dimethylamine < methylamine < ammonia and decreased with increasing catalytic alkalinity. These findings provide new insights for understanding other Cl2O sources beyond the ClONO2 + HOCl reaction.

Integrating Theoretical and Experimental Approaches to Unveil the Mechanical Properties of CuSbSe2 Thin Films

Abstract An exhaustive investigation of the mechanical characteristics of CuSbSe2 (CASe) thin films is conducted in this study by combining experimental nanoindentation methods with theoretical simulations. The Ab-initio Molecular Dynamics (AIMD) calculations are performed with the machine learning (ML) force fields. By employing the Vienna Ab-initio Simulation Package (VASP) based on Density Functional Theory (DFT), theoretical inquiries are carried out to identify crucial parameters, such as bonding characteristics, elastic constants, hardness, bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio. Experimental validation is conducted using nanoindentation to investigate load-dependent hardness and Young’s modulus in a manner that closely matches the theorized predictions. The anomalies between experimental and theoretical outcomes are ascribed to anisotropic behavior and grain boundaries. Furthermore, an investigation is conducted into the directional dependence of sound wave velocities in the CASe films, leading to the revelation of intricate elastic property details. By employing an integrated theoretical-experimental approach, the present attempt not only increases the knowledge concerning CASe films but also fortifies the relationship between theory and experiment, thereby bolstering the dependability of our results. The insights provided as a result of this paper facilitate the development of CASe film applications in a variety of technological fields in the future.&amp;#xD;

Exploring complete catalytic cycle of methane oxidation to methanol on Cu2O2 stabilized within MIL-53(Al) framework: A combined DFT and microkinetic study

Although inspiration from copper-based natural enzymes has shown promise in improving catalyst design for methane-to-methanol (MTM) oxidation, high productivity, and selectivity under mild conditions remain a significant challenge. This study constructs the dinuclear copper (Cu2) species stabilized within the metal-organic framework (MOF), MIL-53(Al), containing Cu as efficient catalytic sites and explores the ability of different oxidants (O2, N2O, and H2O2) to oxidize Cu2 into the dicopper-oxo (Cu2O2) species using density functional theory (DFT) calculations. Our results indicate the kinetic and thermodynamic favorability of Cu2O2 species formation using O2 as an oxidant within the MIL-53(Al) framework. Furthermore, the thermal stability of Cu2O2/MIL-53(Al) has been verified via ab initio molecular dynamics (AIMD) calculations. The kinetics of the complete MTM oxidation cycle over Cu2O2/MIL-53(Al) have been studied using both DFT and microkinetic simulation methods. The present study predicts that the C-H activation on the Cu2O2/MIL-53(Al) has a low free energy barrier (0.77 eV) and that the high stability of CH3 and its very low free energy barrier in the C-O coupling step favors the methanol formation over the formaldehyde. More importantly, Cu2O2/MIL-53(Al) exhibits high methanol selectivity owing to the inhibition of CH3 dehydrogenation and low methanol desorption energy (0.21 eV). Microkinetic simulations confirm the methanol production under relatively mild reaction conditions (200–280 K and 1 bar). This work provides insights into the feasibility of selective MTM oxidation over this family of MOF under mild conditions.

SiP2 monolayer as potential anode material for Na/K-ion batteries predicted from first-principles calculations

Based on the density functional theory (DFT), a systematic feasibility analysis of monolayer SiP2 as potential anode material for Na/K-ion batteries has been carried out. Through ab-initio molecular dynamics (AIMD) calculation, the findings reveal exceptional stability of SiP2. The ultra-low ion diffusion barriers (0.107 eV for Na and 0.043 eV for K) and metallic properties following adsorption of alkali metal ions demonstrate that SiP2 exhibits a rapid charge and discharge rate and remarkable electrical conductivity when employed as an anode. Furthermore, it possesses a considerable theoretical storage capacity (Na/K: 446.53/595.38 mAh/g) and energy density (Na/K: 1026.91/1322.46 mWh/g). These findings suggest that monolayer SiP2 exhibits superior performance as potential anode material for Na/K-ion batteries.

Intramolecular Vibrational Energy Redistribution in the Reaction H3+ + CO → H2 + HCO.

An ab initio direct molecular dynamics (MD) calculation at the RS2/aug-cc-pVQZ level, followed by vibration mapping, has been applied to the H3+ + CO → H2 + HCO+ reaction to elucidate the intramolecular vibrational energy redistribution (IVR) processes during the reaction. Direct MD calculations were carried out for 20 K (a typical temperature for interstellar dark clouds) and 330 K (a typical translational temperature for ions in a glow discharge). Under the Cs symmetry constraint, the approach of H3+ turned out to be the H-C stretching mode of the [H···CO]+ part, which invoked the C-O stretching and then the H-C-O bending modes. Under no symmetry constraint, a strong bending mode was first invoked, and the intensities of the subsequent H-C and C-O stretching modes were kept relatively small. The detailed analyses of the IVR during the reaction, in terms of vibration mixing, gave a clue to understanding experimentally observed anomalies in the bending modes, such as population inversion at some bending states. In the MD simulation at 20 K, less than two-thirds of the reaction energy was converted to the vibrational energy of the resultant HCO+ part and one-third to the translational and rotational energies of the leaving H2 molecule. These direct MD simulations, when combined with the experimental spectroscopy data, shed light on a clear understanding of the reaction mechanism, including the IVR during the reaction.

Exploring the Mechanisms of LiNiO2 Cathode Degradation by the Electrolyte Interfacial Deprotonation Reaction.

Nickel-rich layered oxides stand as ideal cathode candidates for high specific capacity and energy density next-generation lithium-ion batteries. However, increasing the Ni content significantly exacerbates structural degradation under high operating voltage, which greatly restricts large-scale commercialization. While strategies are being developed to improve cathode material stability, little is known about the effects of electrolyte-electrode interaction on the structural changes of cathode materials. Here, using LiNiO2 in contact with electrolytes with different proton-generating levels as model systems, we present a holistic picture of proton-induced structural degradation of LiNiO2. Through ab initio molecular dynamics calculations based on density functional theory, we investigated the mechanisms of electrolyte deprotonation, protonation-induced Ni dissolution, and cathode degradation and the impacts of dissolved Ni on the Li metal anode surfaces. We show that the proton-transfer reaction from electrolytes to cathode surfaces leads to dissolution of Ni cations in the form of NiOOHx, which stimulates cation mixing and oxygen loss in the lattice accelerating its layered-spinel-rock-salt phase transition. Migration of dissolved Ni2+ ions to the anode side causes their reduction into the metallic state and surface deposition. This work reveals that interactions between the electrolyte and cathode that result in protonation can be a dominant factor for the structural stability of Ni-rich cathodes. Considering this factor in electrolyte design should be of benefit for the development of future batteries.

Construction of Al–Si interatomic potential based on Bayesian active learning

Nanoscale simulations for optimizing the performance and processing of Al–Si alloys are currently facing two major obstacles: the scarcity of high-quality semi-empirical potentials tailored to complex alloy systems, and the prohibitively high computational cost associated with ab initio molecular dynamics simulations. In order to enhance simulation efficiency and accuracy of the Al–Si alloys’ microstructural evolution, this study employs a dynamic active learning technique, FLARE, to develop a non-parametric machine learning potential that combines the high accuracy of density functional theory (DFT) with the efficiency of classical molecular dynamics (MD). Without relying on extensive initial ab initio molecular dynamics data or existing databases, collection of the necessary data is progressively made during the active learning process, thereby constructing a potential capable of accurately simulating the structure and dynamics of high-temperature Al–Si alloys. By comparing with experimental measurements and ab initio molecular dynamics calculations, the high accuracy and computational efficiency of this potential is demonstrated in predicting energy, force, structure, and dynamic properties. The results provide novel theoretical insights for optimizing Al–Si alloy processing and underscore the usefulness of active learning methods in constructing high-accuracy potentials.

Harnessing MBene termination for superior anode interfaces in Li/Ca-ion batteries

The elevation of two-dimensional (2D) transition metal borides, specifically MBenes, as anode materials for lithium-ion batteries (LIBs) and calcium-ion batteries (CIBs) can be achieved through strategic functionalization with appropriate groups. Utilizing a first-principles approach, we conducted an in-depth investigation into the electrochemical properties of chlorine-terminated V2B (V2BCl2) as a candidate anode material for LIBs and CIBs. V2BCl2 exhibits metallic behavior, as demonstrated by band structure analysis, which endows it with exceptional conductivity due to the free electron surface of the system, thereby embodying ideal anode characteristics. The dynamic and thermal stability of the system was assessed through comprehensive phonon dispersion analyses and ab-initio molecular dynamics (AIMD) calculations. High net charge transfer rates of Li/Ca ions towards the monolayer, augmented electron localization function (ELF) near system atoms, and the presence of ionic bonds between Ca/Li and the V2BCl2 monolayer contribute to the enhanced conductivity observed in these anode systems. This is corroborated by metrics such as the projected crystal orbital Hamiltonian population (-pCOHP), low diffusion energy barriers (< 0.35 eV) facilitating rapid charging mechanisms, and low open circuit voltages (< 0.32 V) ensuring robust battery performance stability. Furthermore, V2BCl2 exhibits notable specific storage capacities of 875.67 mAh g−1 for Ca ions and 1167.75 mAh g−1 for Li ions, surpassing the benchmarks set by recent MBene systems. These promising results strongly advocate for V2BCl2 as a viable candidate for anode material in both LIB and CIB applications, highlighting its potential significance in advancing battery technology.

Predicting Reactivity and Passivation of Solid-State Battery Interfaces.

In this work, we build a computationally inexpensive, data-driven model that utilizes atomistic structure information to predict the reactivity of interfaces between any candidate solid-state electrolyte material and a Li metal anode. This model is trained on data from ab initio molecular dynamics (AIMD) simulations of the time evolution of the solid electrolyte-Li metal interfaces for 67 different materials. Predicting the reactivity of solid-state interfaces with ab initio techniques remains an elusive challenge in materials discovery and informatics, and previous work on predicting interfacial compatibility of solid-state Li-ion electrolytes and Li metal anodes has focused mainly on thermodynamic convex hull calculations. Our framework involves training machine learning models on AIMD data, thereby capturing information on both kinetics and thermodynamics, and then leveraging these models to predict the reactivity of thousands of new candidates in the span of seconds, avoiding the need for additional weeks-long AIMD simulations. We identify over 300 new chemically stable and over 780 passivating solid electrolytes that are predicted to be thermodynamically unfavored. Our results indicate many potential solid-state electrolyte candidates have been incorrectly labeled unstable via purely thermodynamic approaches using density functional theory (DFT) energetics, and that the pool of promising, Li-stable solid-state electrolyte materials may be much larger than previously thought from screening efforts. To showcase the value of our approach, we highlight two borate materials that were identified by our model and confirmed by further AIMD calculations to likely be highly conductive and chemically stable with Li: LiB13C2 and LiB12PC.

First principles study of Perfluoroalkyl substance adsorption in [formula omitted]-MOF-74 metal organic frameworks

Perfluoroalkyl substances (PFAS) are a family of chemical species consisting of a perfluorinated C-F bonded backbone, granting high thermal and aqueous stability. However, as they have been found to cause deleterious health effects in humans, their lack of degradation in air or water has led to the desire for new remediation technology, and absorptive removal by porous materials has been found to be a promising way to accomplish this. In this work, we investigate the metal organic framework (MOF) family known as M-MOF-74 (M = Cu, Mg, Zn, Pt) as potential adsorbents for the PFAS molecules PFOA, PFOS, and TFA. Using a combination of density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations, we find that protonated PFAS molecules can adsorb strongly in the M-MOF-74 frameworks, and that changing the M site results in tunability of the adsorption energy. Second, we find that, given the same length of the C backbone, those terminated by a -COOH group versus a -SO3H group binds more strongly; furthermore, the C backbone length has an effect as well, with long-chain PFAS adsorbing more strongly than short-chain. Finally, we find that deprotonated PFAS molecules do not interact with MOF compounds and display a positive adsorption energy, with Bader charge calculations show a distinct difference between protonated and deprotonated PFAS molecules. Through this work, we disentangle how MOF and PFAS chemistry affects adsorption in this family of compounds.

Prediction of Two-Dimensional Janus Transition-Metal Chalcogenides: Robust Ferromagnetic Semiconductor with High Curie Temperature.

Two-dimensional (2D) ferromagnetic semiconductors (FM SCs) provide an ideal platform for the development of quantum information technology in nanoscale devices. However, many developed 2D FM materials present a very low Curie temperature (TC), greatly limiting their application in spintronic devices. In this work, we predict two stable 2D transition metal chalcogenides, V3Se3X2 (X = S, Te) monolayers, by using first-principles calculations. Our results show that the V3Se3Te2 monolayer is a robust bipolar magnetic SC with a moderate bandgap of 0.53 eV, while V3Se3S2 is a direct band-gap FM SC with a bandgap of 0.59 eV. Interestingly, the ferromagnetisms of both monolayers are robust due to the V-S/Se/Te-V superexchange interaction, and TCs are about 406 K and 301 K, respectively. Applying biaxial strains, the FM SC to antiferromagnetic (AFM) SC transition is revealed at 5% and 3% of biaxial tensile strain. In addition, their high mechanical, dynamical, and thermal stabilities are further verified by phonon dispersion calculations and ab initio molecular dynamics (AIMD) calculations. Their outstanding attributes render the V3Se3Y2 (Y = S, Te) monolayers promising candidates as 2D FM SCs for a wide range of applications.

Crystal facet/interface anchored Janus activity of BiOBr in driving photocatalytic water splitting

Constructing Janus junctions is expected to provide a novel perspective for analyzing the intrinsic photocatalytic activity of bismuth oxyhalide. Herein, Janus-typed BiOBr(010)/BiOBr(001) homojunction with efficiently photocatalytic H2 evolution has been achieved by a hydrothermal synthesis. The experimental results show that the designed Janus-typed junction can effectively elevate the carrier lifetime, significantly enhance the photocurrent, and prominently reduce the overpotential. The potential difference (0.34 eV) between (010) facet and (001) facet can drive the carrier transport at the interface for Janus junctions. Theoretical calculations indicate that the designed Janus junction has a stable mechanical structure, providing certain support for the long lifetime of the photocatalyst in the photocatalytic process. The carrier distributions in the Janus junction exhibit the typical characteristic distribution. Interestingly, the photo-generated electrons are only localized in BiOBr(001) component, which embodies significantly a role of n-type semiconductor. This essentially activates HER activity (32 µmol/h g−1) of Janus junction. The holes preferentially localize in the BiOBr(010) component of Janus junction. This component undertaking p-type role reduces the free energy of the rate determining step (from OH* to O*) in the oxygen evolution process (0.88 eV). The Janus junction intensively suppresses the carrier recombination probability at the high symmetry point (reciprocal space) in BiOBr. Ab initio molecular dynamics calculations show that the adsorbed water is easy to decompose on the surface of Janus junction. The obtained results of the photocatalytic water splitting further confirm that the designed BiOBr(010)/BiOBr(001) has Janus characteristics, which are consistent with theoretical calculations and tracer tracing results. The diffusion characteristics of hydrogen also evidence that the interaction of the internal electric field in the Janus junction can drive the HER performance. Additionally, these results offer us a unique angle of view to regulate the charge carrier dynamics by the highly oriented facet coupling for the layered semiconductor.

(Invited) Large Electromechanical Coupling in Zr-Doped Ceria

The catalytic, ion-transport and chemo-mechanical properties of Zr-doped ceria have been the subjects of broad ranging investigation by the materials research community. Yet, until recently, electromechanical coupling in ZrxCe1-xO2-δ has not been studied: ZrxCe1-xO2-δ ceramics were not expected to be electromechanically active. We have investigated the electrostriction (ES) effect, a second order electromechanical response, i.e., strain, u , is proportional to M·E 2, where E is the applied electric field and M is the longitudinal electrostriction strain coefficient. Large electrostriction in ceria has generally been associated with oxygen vacancies (Vo) which provide charge compensation for aliovalent dopants or for cerium reduction (Ce3+). The electrostriction effect induced by oxygen vacancies is restricted to frequency <1 Hz and is characterized by low saturation strain (|usat| <15 ppm).By contrast, isovalent doping with Zr (unexpectedly) results in a large electrostriction strain coefficient, reaching |M|=10-16 m2/V2 for x=0.1. This effect persists to frequency ≥3 kHz with |u| ≥220 ppm, making Zr0.1Ce0.9O2 competitive with the best commercial electrostrictor (PMN-PT15), but with ~100 times lower dielectric constant and three-fold higher elastic modulus. XAS data, DFT modelling and ab initio molecular dynamics (AIMD) calculations demonstrate that, unlike the permanent, but orientationally labile, elastic dipoles (i.e. local distortions with symmetry lower than that of the host lattice) formed by oxygen vacancies, elastic dipoles formed by Zr-doping are dynamic. In the absence of an E-field, [ZrO8]-local bonding units remain, on average, centered with respect to the second (cation) coordination shell. Due to bond anharmonicity, however, displacement of Zr by an anisotropic E-field requires less energy than displacement of the host cations, resulting in a large dynamic elastic dipole. This polarizable elastic dipole gives rise to large electrostrictive strain and constitutes the first example of non-classical electrostrictors (NCES) relying solely on substitutional point defects. In fact, a relatively small, isovalent dopant cation, such as Zr, along with nearest neighbor anions, vibrating anharmonically in a relatively large cage (compared to that of the host cation) may in fact facilitate electromechanical coupling.|M| of Zr-doped ceria increases exponentially with Zr content for x=0-0.1, suggesting that the contribution of Zr-ions to electrostrictive strain may not be simply additive. Zr-doping also increases the relative dielectric permittivity at 100Hz, from ~26 (x=0), to ~220 (x=0.1) and lowers the elastic modulus from 227GPa (x=0) to 214GPa (x=0.1), even though the number of chemical bonds remains unchanged. AIMD calculations report that stiffness for moving [CeO8]-local bonding units is essentially isotropic and is 2-2.4 times higher than for [ZrO8]. Stiffness for moving [CeO8] first nearest neighbor to Zr, is only slightly decreased from that in the bulk. These results can provide the theoretical basis for the reduction of the Young’s modulus and increase in the dielectric permittivity with Zr doping.When the concentration of Ce3+ is ≥ 100 ppm in ZrxCe1-xO2-δ, ( i.e., the material has not been completely re-oxidized), accompanied by the formation of oxygen vacancies (VO) for charge compensation, electrical conductivity is increased and electrostriction is suppressed. In addition, by co-doping Zr0.1Ce0.9O2 with 0.5mol% of aliovalent cations - Ca, Sc, Yb or La - we observed that the aliovalent dopant reduces the electrostriction strain coefficient by more than an order of magnitude and restores the values of Young’s modulus and dielectric permittivity to values close to those of undoped ceria. Since all these co-dopants, irrespective of valence and ionic radius, lead to a similar result, we concluded that the species responsible for the suppression of electrostriction in Zr doped ceria must be the oxygen vacancies. This finding is supported by XAS measurements and AIMD calculations. Fourier transform of Zr K-edge EXAFS spectra reveal that, even though the molar ratio ZrCe:VO is 40:1 in the co-doped compounds, oxygen vacancies nevertheless succeed in introducing enhanced disorder into the second coordination shell (cation) of Zr. DFT modelling predicts that a [ZrO7-VO] local bonding unit is stiff and asymmetrically distorts adjacent unit cells, leading to an elastic interaction length in the lattice between Zr-ions ≥ two-and-a-half-unit cells, which, in the absence of oxygen vacancies, can allow limited collective motion. However, such collective motion does not lead to a phase transition even at 123 K, implying that interaction between Zr-ions is neither sufficiently strong nor sufficiently long-range to produce freezing of the displacement, an effect that has been observed for perovskite relaxors.

(Invited) Tuning Selective CO2 Electrohydrogenation Under Mid Temperature and Pressure

To address rising environmental concerns and energy challenges, it is highly desirable to develop green technologies for a sustainable future. Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds. Electrochemical CO2 hydrogenation using renewable electricity is considered one of the most promising pathways to reach the environmental economics. Among various electrochemical devices, a solid state electrolyzer working at intermediate temperatures has the advantages of high reaction rates and low overpotentials. As CO2 molecules is quite stable, it is critical to develop electrocatalysts with high activity to reduce electricity engagement. Also, CO2 hydrogenation has multiple pathways which normally results in low selectivity for a target product. A tunable electrocatalyst with high selectivity to different products is desirable for CO2 conversion reactions. Heterostructured nanomaterials attracts great attentions in electrochemical systems. With careful design, they can show very high activity and selectivity towards an electrochemical reaction pathway. In this work, we combine theoretical simulations, including density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations, with experimental methods (characterizations and electrochemical measurements) for rational design of highly efficient heterostructured nanomaterials for CO2 hydrogenations. We studied the strong metal-support interaction (SMSI) in a doped CeO2 supported noble metal nanoparticles (NPs) system using theoretical calculations. The results indicate that SMSI largely depends on chemical conditions of the support and particle size of dispersed metal NPs. By tuning the SMSI, we can successfully change the catalytic activity and selectivity towards CO2 hydrogenation reactions. Based on these findings, we designed tunable heterostructured nanomaterials for efficient hydrogenation reactions at intermediate temperatures. These predictions were further confirmed by experimental method. By using a combination of high-throughput theoretical calculations and electrochemical measurements, we successfully developed highly active catalysts for electrochemical CO2 hydrogenation reactions. This framework is also applicable to other electrochemical systems using heterostructured materials.

Vanadium Oxides in Neuromorphic Computing: Unveiling Insights through First Principles Calculations

Neuromorphic computing represents a revolutionary approach to developing analog non-volatile memory (NVM) devices. This technology relies on electron-correlated materials capable of replicating the functioning of synapses and neurons in the brain, making it ideal for energy-efficient parallel computing applications. Among the myriad of innovative materials suitable for neuromorphic computing, such as conductive polymers, organic semiconductors, and nanowires, among others, electron-correlated transition metal oxides stand out for their ability to undergo metal-insulator transitions either by tuning their oxygen content or the stoichiometry of an intercalating metal ion. In this talk we discuss from a first principles perspective the pivotal role that vanadium oxide has the potential to play in the development neuromorphic computing devices. First, we examine the use of vanadium oxide as a Mott insulator capable of undergoing a stable phase separation process that is suitable for non-volatile electrochemically activated random access memory devices (ECRAM). A stable phase coexistence across multiple segregated vanadium oxides states provides the device the ability express non-volatile memory behavior after precise tunning of oxygen vacancies into VO2. The correlation between these oxides’ formation energies and their oxygen content provides clues on the stable formation of coexisting crystalline phases that provide tunable resistivity based on the relative fraction and distribution of each phase with unusual retention, with an estimated 1% loss over 14 years in ambient conditions. Second, we address the structural and electrical properties of β’-CuxV2O5 based on temperature and Cu content. Ab-initio molecular dynamics calculations provide a close-up view of the correlation between Cu content and mobility and its ability to induce structural distortions to the intercalating β’-CuxV2O5 host that spike close to the insulator-metal transition (IMT).

Ab Initio Molecular Dynamics Insight to Structural Phase Transition and Thermal Decomposition of InN.

Extensive ab initio density functional theory molecular dynamics calculations were used to evaluate stability conditions for relevant phases of InN. In particular, the p-T conditions of the thermal decomposition of InN and pressure-induced wurtzite-rocksalt solid-solid phase transition were established. The comparison of the simulation results with the available experimental data allowed for a critical evaluation of the capabilities and limitations of the proposed simulation method. It is shown that ab initio molecular dynamics can be used as an efficient tool for simulations of phase transformations of InN, including solid-solid structural transition and thermal decomposition with formation of N2 molecules. It is of high interest, because InN is an important component of epitaxial quantum structures, but it has not been obtained as a bulk single crystal. This makes it difficult to determine its basic physical properties to develop new applications.

Electrochemical Stability of MXenes in Water Based on Constant Potential AIMD Simulations.

MXene has been recently explored as promising electrocatalytic materials to accelerate the electrocatalytic process for hydrogen evolution, but their dynamic stability under electrochemical conditions remains elusive. Here we performed first-principle ab initio molecular dynamics calculations to reveal the electrochemical stability of Ti2CTx MXene in different aqueous environments. The results revealed the high vulnerability of the pure and vacancy-defected Ti2CO2 MXene towards water attack, leading to surface oxidation of MXene under neutral electrochemical condition that formed adsorbed oxygen species to Ti and dissociated proton in solution. The surface oxidation of Ti2CO2 could be prevented in the acid condition or in the neutral condition under the negative potential. Differently, the fully F- or OH-functionalized Ti2CF2 and Ti2C(OH)2 as well as the mixed functionalized Ti2C(O0.5OH0.5)2 and Ti2CO1.12F0.88 are highly stable under various electrochemical conditions, which can effectively prevent close contact between water and surface Ti atoms via electronic repulsion or steric hindrance. These findings provide atomic level understanding of the aqueous stability of MXene and provide useful strategies to prevent degradation and achieve highly stable MXenes.

MoSSe/Si9C15 heterojunction photodetectors with ultrahigh photocurrent and carrier mobility

The structural, electronic, optical properties and photogalvanic effect of MoSSe/Si9C15 and Si9C15/MoSSe heterostructures are investigated utilizing density functional theory. Band gaps of 1.70 eV and 1.03 eV are respectively exhibited by these heterostructures, both classified as direct bandgap semiconductors. The thermal stability of the MoSSe/Si9C15 and Si9C15/MoSSe heterostructures is demonstrated through ab initio molecular dynamics calculations. A hole mobility of 62774 cm2/Vs in the zigzag direction and an electron mobility of 1248 cm2/Vs in the armchair direction are recorded for the MoSSe/Si9C15 heterostructure. Light absorption in both the ultraviolet and visible light regions is observed for these heterostructures. Upon construction of a self-powered MoSSe/Si9C15 photodetector, a peak photocurrent (Jph) of 10.76 a02/photon is achieved, influenced by changes in polarization angle θ and photon energy, and a maximum extinction ratio of 26.7 is reached, showcasing high polarization sensitivity.

Hydrogen adsorption, migration and desorption on amorphous carbon: A DFT and AIMD study

Physisorption is the general dominating adsorption mode on pure carbonaceous materials. In this study, we examined if chemisorbed hydrogen can be accomplished without incorporating metals on carbon surfaces. We constructed two 100-atom amorphous carbon (a-C) models with different microenvironments (42 % 2-fold, 52 % 3-fold, and 6 % 4-fold coordinated carbon atoms and 18 % 2-fold and 82 % 3-fold, respectively) using ab initio molecular dynamics (AIMD) simulations to mimic activated carbon samples in reality. The structural, energetic, electronic structure and kinetic properties of hydrogen adsorption, migration, and desorption on the a-C surfaces were analyzed using density functional theory (DFT) and AIMD calculations, which showed that: (1) hydrogen molecules could spontaneously dissociate on the convex side of 2-fold coordinated carbon atoms. Physisorption of hydrogen molecules mainly took place on 3-fold coordinated carbon atoms. (2) Regarding the multiple hydrogen adsorption, the entire a-C model could uptake around 156 hydrogen atoms with the adsorption energy per hydrogen atom about −0.70 to −0.60 eV at high hydrogen pressure. In addition, we found that the average individual adsorption energy of a single hydrogen atom on different carbon atoms could be used as a quick prediction for the saturated hydrogen adsorption energy. (3) The migration barrier of a hydrogen atom between two adjacent carbon atoms was about 2 eV at both low and high hydrogen coverage, indicating that hydrogen mobility on this designed a-C model was low. The desorption of a hydrogen molecule can take place at 300 K using AIMD calculation, but not for atomic hydrogen desorption. In this work, we demonstrated that hydrogen chemisorption could take place on this designed a-C without the decoration of metal particles to enhance hydrogen adsorption amounts. The materials design to balance hydrogen chemisorption, migration, and desorption shall be considered in the future.

Effect of nitrogen-containing groups on the reduction of copper ions: In situ Raman and AIMD

In situ Raman spectroscopy and ab initio molecular dynamics (AIMD) were utilized to observe and analyze the micro-scale variations of levelers on the cathode surface. The cathodic polarization and charge transfer resistance of the three electroplating systems were examined using electrochemical methods. The throwing power of the printed circuit board coating and the nucleation changes at various times were investigated using an OLYMPUS confocal laser microscope and a scanning electron microscope. Based on the first-principles and AIMD calculations, the energy gaps, adsorption energies, and dynamic changes over 20 ps for the three levelers were determined, and the molecular mechanisms of action on the copper surface were analyzed to demonstrate alterations in the coating thickness. Experimental and theoretical results indicate that 2-thiazole-2-thiol possesses the strongest inhibitory energy, significantly repelling copper ions from migrating to the far end. On the surface, 4,6-dimethyl-2-pyrimidinethiol decomposes to form nitrogenous and sulfurous groups, which inhibit and adsorb copper ions. The adsorption states of the three levelers were thoroughly validated using Raman spectroscopy, corroborating the AIMD simulation results.