Ab Initio Molecular Dynamics Simulations Research Articles

Understanding the adsorption of imidazole corrosion inhibitor at the copper/water interface by ab initio molecular dynamics

Understanding the adsorption mechanisms of organic corrosion inhibitors at metal/water interfaces is crucial for designing corrosion inhibitors. Imidazole adsorption at copper/water surfaces was investigated via ab initio molecular dynamics simulations. The adsorption energy of imidazole on copper in water is slightly more positive than that in vacuum, which is attributed to the hydrogen bond interaction between imidazole and water molecules. Imidazole adsorption changes interfacial water density and dipole distribution, disrupts hydrogen bond networks, and decreases water residence time at the interface. These characteristics are considered to be correlated to the decreased corrosion rate induced by imidazole adsorption.

Computational prediction of two dimensional Mo4BC as promising anode material for lithium-ion batteries

The rising demand for high-capacity energy storage systems drives the hunt for cutting-edge lithium-ion batteries. Herein, calculations based on density functional theory have been performed to investigate the properties of two-dimensional (2D) Mo4BC monolayer as an anode material with high stability and storage capacity. Phonon dispersion and ab initio molecular dynamics (AIMD) simulations were performed to determine the dynamic and thermal stability, respectively. A low diffusion barrier of 0.12 eV supports the ultrahigh ionic mobility of Li ions and cycling capability for this material, which is essential for the fast charging/discharging process. In addition, the Li-ion adsorption on Mo4BC shows a high capacity of about 800 mAhg−1 with an average open circuit voltage (Vocv) of 0.03 V. Comprehensive overview of Mo4BC as high-capacity anode material with negligible low diffusion barrier and metallic character provides a significant contribution towards the advancement of energy storage systems such as lithium-ion batteries (LIBs). Our findings suggest Mo4BC as a promising anode material for high-performance LIBs, thus offering valuable insights for exploring innovative anode materials.

Amorphous boron carbonitride (BC4N) from ab initio simulations

This study utilizes ab initio molecular dynamics simulations to explore the structure and properties of amorphous boron carbonitride (a-BC4N). A 432-atom model, generated via a conventional melt-and-quench technique, exhibits a graphite-like structure with all elements possessing an average coordination number of about 3.0. C atoms dominate within individual layers, interspersed with distinct BN domains. This atomic arrangement deviates considerably from that proposed for crystalline BC4N structures. Despite this structural variation, the a-BC4N model is likely a narrow band gap semiconductor (0.15 eV), similar to its crystalline counterparts. In terms of mechanical properties, a-BC4N demonstrates similarities with various layered materials while exhibiting a notably larger bulk modulus.

The first-principles study of 2D monolayer T-Mo2C as promising anode material for Lithium-ion Batteries

The growing demand for renewable energy technologies emphasizes the necessity for advancements in anode materials to enhance the performance of lithium-ion batteries (LIBs). In this research, we employ first-principles calculations to investigate the properties of a T-Mo2C monolayer proposed as an anode material. Phonon dispersion calculations and ab initio molecular dynamics (AIMD) simulations are conducted to assess the dynamical stability and thermal characteristics of the T-Mo2C monolayer as an anode material. Remarkably low diffusion barriers of 0.029 eV (Li) and 0.01 eV (Na and K) have been identified, facilitating rapid ion mobility. Furthermore, a monolayer of metal ions (M = Li, Na, K) absorbed onto T-Mo2C is explored, revealing a high specific capacity of approximately 1314.37 mAh/g (Li), 262.87 mAh/g (Na), and 32.85 mAh/g (K). The average open circuit voltage is determined to be 0.08 V (Li), 0.68 V (Na), and 2.59 V (K). This research provides a comprehensive overview of T-Mo2C monolayer as a high-capacity anode material, emphasizing its significant contributions to advancing energy storage systems, particularly in the context of LIBs. The findings presented here pave the way for the development of efficient and sustainable energy storage solutions to meet the escalating demands of the renewable energy landscape.

Weakly Hydrated Solute of Mixed Hydrophobic-Hydrophilic Nature.

Infrared (IR) spectroscopy is a commonly used and invaluable tool in studies of solvation phenomena in aqueous solutions. Concurrently, density functional theory calculations and ab initio molecular dynamics simulations deliver the solvation shell picture at the molecular detail level. The mentioned techniques allowed us to gain insights into the structure and energy of the hydrogen bonding network of water molecules around methylsulfonylmethane (MSM). In the hydration sphere of MSM, there are two types of populations of water molecules: a significant share of water molecules weakly bonded to the sulfone group and a smaller share of water molecules strongly bonded to each other around the methyl groups of MSM. The very weak hydrogen bond of water molecules with the hydrophilic group causes the extended network of water hydrogen bonds to be not "anchored" on the sulfone group, and consequently, the MSM hydration shell is labile.

Strain hardening and toughening in metal/molecular nanolayer/metal nanosandwiches

Introducing molecular nanolayers (MNLs) is attractive for enhancing the stability of, and inducing unusual properties at, inorganic thin film interfaces. Although organic molecules anchored to inorganic surfaces have been studied extensively, property enhancement mechanisms underpinned by molecular assemblies at inorganic thin film interfaces are yet to be revealed and understood. Here, ab initio molecular dynamics simulations of tensile strain of Au/MNL/Au thin film nanosandwich models provide insights into molecularly induced strain hardening and toughening. Au/MNL/Au nanosandwiches support up to ≈30% higher stresses and exhibit up to ≈140% higher toughness than pure Au slab models. Both hardening and toughening are governed by molecular length and terminal chemistry in the MNL. Strong Au/MNL interface bonding and greater molecular length promote defect creation in Au, which results in strain hardening. Accommodation of increasing post-hardening strains in the MNL mitigates the stress increase in the Au slabs, delays interface fracture, and contributes to toughening. Remarkably, toughening correlates with equilibrium interface strain, which could be used as a proxy for efficiently identifying promising inorganic/MNL combinations that provide toughening. Our findings are important for the discovery and design of inorganic–organic interfaces, nanomaterials, and composites.

Transition Metal (Cu, Pd, and Ag)-Modified Nb2S2C Monolayer for Highly Efficient Catechol Sensing: A First-Principles Investigation.

Motivated by recent advancements and the escalating application of two-dimensional (2D) gas or molecule sensors, this study explores the potential of the 2D Nb2S2C monolayer for detecting biomolecule catechol (Cc), whose excess concentration is highly dangerous to living beings. We use first-principles density functional theory (DFT) calculations to assess the Cc sensing performance of pure and transition metal (TM = Cu, Pd, Ag)-modified Nb2S2C monolayers. The Nb2S2C monolayer belonging to the new class of synthesized 2D materials, TM carbo-chalcogenides (TMCC), combines distinctive properties from both TM dichalcogenides and TM carbides and exhibits physisorption (-0.66 eV) toward the Cc molecule. Notably, the surface modifications with these TMs significantly enhanced the adsorption energy of Cc. The chemisorption of the Cc molecule on the Pd to Cu-modified monolayer is demonstrated with adsorption energies ranging from -1.09 to -1.3 eV and is due to the robust charge transfer and orbital interactions between the valence orbitals of TMs and Cc. In addition, the modification of the surface by TM leads to an increased work function sensitivity toward the Cc molecule. The study establishes the thermal stability at 300 K and dynamic stability of TM-Nb2S2C through ab initio molecular dynamics (AIMD) simulations and Phonon calculations, respectively. The theoretical estimation of achievable recovery time at 400 and 450 K for Pd and Ag and at 500 K for the Cu-modified Nb2S2C monolayer, respectively, confirms the potential practical application of the sensor for Cc detection. These compelling characteristics position the Nb2S2C monolayer as a promising nanomaterial for detecting Cc molecules in the environment.

Partitioning of Iron Between (Mg,Fe)SiO3 Liquid and Bridgmanite

AbstractThe evolution of the magma ocean that occupied the early Earth is influenced by the buoyancy of crystals in silicate liquid. At lower mantle pressures, silicate crystals are denser than the iso‐chemical liquid, but heavy elements like iron can cause crystals to float if they partition into the liquid phase. Crystal flotation allows for a basal magma ocean, which might explain geochemical anomalies in mantle‐derived magmas, seismic anomalies in the lower mantle, and the source of the Earth's early magnetic field. To examine whether a basal magma ocean is gravitationally stable, we investigate the degree of iron partitioning between (Mg,Fe)SiO3 liquid and bridgmanite. By utilizing ab initio molecular dynamics simulations coupled with thermodynamic integration, we find that iron partitions into the liquid, and increasingly so with increasing pressure. Bridgmanite crystals are found to be buoyant at lower mantle conditions, stabilizing the basal magma ocean.

Structural properties and aromaticity of rare-earth doped tin cluster anion: MSn9− (M = Sc, Y, La)

Doping rare earth elements into clusters can significantly improve the performance and application value of the materials. The structure, bonding properties, stability, and aromaticity of MSn9− (M = Sc, Y, La) have been investigated using density-functional theory. The global minimum structure of these clusters is determined to be the addition of a triangle to the vertex position of a pentagonal bipyramid. Ab initio molecular dynamics simulations are used to demonstrate the thermal stability of the structure. Bonding analyses indicate the presence of ionic bonding and covalent bonding. Iso-chemical shielding surfaces and the gauge-including magnetically induced currents indicate that MSn9− clusters are significantly aromatic. This study provides a comprehensive understanding of tin-based nanomaterials, which is important for their design and synthesis.

Hydrogen adsorption and dissociation, together with a multifractal transition into graphene-based surfaces

Ab-initio molecular dynamics simulations, together with multifractal detrended fluctuation analysis (MF-DFA) were used to study hydrogen adsorption into a five-vacancy graphene surface. This surface was chosen because it presents active bonds, due to a lack of carbon ions and may thus be appropriate for molecular hydrogen adsorption and storage. Hydrogen dissociation and chemical hydrogen adsorption, together with a multifractal transition were observed at the beginning of molecular dynamics simulations. Multifractal phase transition is a consequence of hydrogen dissociation and adsorption and was observed in the multifractal spectrum, as a fishtail-like behavior. Once the molecular hydrogen was adsorbed and dissociated, a weak multifractal spectrum was observed in time-series. Weak multifractal behavior was adduced by comparing to fractional Brownian motion (FBM). Multifractal characterization indicates irregular signals and anti-persistence, caused by temperature. A fractional Brownian motion region for forecasting and benchmarking, based on statistical indicators and multifractal characterization of the test region is proposed. The results obtained in this investigation may be significant in the search for surfaces and strategies for hydrogen storage.

Stable, while Still Active? A DFT Study of Cu, Ag, and Au Single Atoms at the C3N4/TiO2 Interface.

Hybrid DFT calculations are employed to compare the adsorption and stabilization of Cu, Ag, and Au atoms on graphitic C3N4 and on the heterojunction formed by g- C3N4 and TiO2. While Cu and Ag can be strongly chemisorbed in form of cations on g- C3N4, Au is only weakly physisorbed. On g- C3N4/TiO2, all coinage metal adatoms can be strongly chemisorbed, but, while Cu and Ag forms cations, Au form an Au- species. Ab Initio Molecular Dynamics simulations confirm that the metal adatoms on g-C3N4 are highly mobile at room temperature, while they remain confined in the interfacial spacing between C3N4 and TiO2 on the heterojunction, being both stably bound and reachable for the reactants in a catalytic cycle. Doping g- C3N4/TiO2 with metal single atoms permits thus to generate catalytic systems with tunable charge and chemical properties and improved stability with respect to bare C3N4. Moreover, the changes in the electronic structure of g- C3N4/TiO2 induced by the presence of the metal single atoms are beneficial also for photocatalytic applications.

First-principles study of 3D porous penta-graphene as anode materials for alkali metal-ion batteries

Porous structure with larger specific surface area is more conducive to ion diffusion for the anode materials of metal-ion batteries. In this work, some 3D porous structures with larger and more pores in three directions were designed based on 2D penta-graphene (PG) nanoribbons. By systematically calculations, it was found two of them (h-PG40 and o-PG36) are both thermally and mechanically stable, even at such high temperatures of 1000 K. The alkali metal-ions of Li, Na, and K can be absorbed and diffuse in the pores of h-PG40/o-PG36, and all the porous structures remain metallic regardless of adsorbed ions. Using ab initio molecular dynamics (AIMD) simulation, the diffusion coefficients of Li, Na, and K at different temperatures were calculated. It is found that Li ions can rapidly diffuse in h-PG40 along three directions, but alkali metal-ions of Na and K with larger radii can rapidly diffuse along larger pores in both structures, and have good rate performance. Based on the diffusion coefficients, the obtained diffusion barriers of Li, Na, and K in the h-PG40/o-PG36 structures were 0.19/0.27, 0.26/0.17, 0.41/0.27 eV, which are considerably smaller compared to the minimum diffusion barrier observed in graphite. As the anode of LIB/SIB/PIB, the theoretical specific capacities of h-PG40 and o-PG36 are above 1451.67/781.67/781.67 and 1116.67/868.52/496.30 mAh·g−1, respectively, and the calculated OCV of both structures are smaller than 1.5 V. This reflects their good specific capacity and cycling performance. This theoretical exploration may open a new frontier in searching more practical 3D porous structures as anode materials for alkali metal-ion batteries.

Highly Efficient Acidic Electrosynthesis of Hydrogen Peroxide at Industrial-Level Current Densities Promoted by Alkali Metal Cations.

Acidic H2O2 synthesis through electrocatalytic 2e- oxygen reduction presents a sustainable alternative to the energy-intensive anthraquinone oxidation technology. Nevertheless, acidic H2O2 electrosynthesis suffers from low H2O2 Faradaic efficiencies primarily due to the competing reactions of 4e- oxygen reduction to H2O and hydrogen evolution in environments with high H+ concentrations. Here, we demonstrate the significant effect of alkali metal cations, acting as competing ions with H+, in promoting acidic H2O2 electrosynthesis at industrial-level currents, resulting in an effective current densities of 50-421 mA cm-2 with 84-100 % Faradaic efficiency and a production rate of 856-7842 μmol cm-2 h-1 that far exceeds the performance observed in pure acidic electrolytes or low-current electrolysis. Finite-element simulations indicate that high interfacial pH near the electrode surface formed at high currents is crucial for activating the promotional effect of K+. In situ attenuated total reflection Fourier transform infrared spectroscopy and ab initio molecular dynamics simulations reveal the central role of alkali metal cations in stabilizing the key *OOH intermediate to suppress 4e- oxygen reduction through interacting with coordinated H2O.

Highly Efficient Acidic Electrosynthesis of Hydrogen Peroxide at Industrial‐Level Current Densities Promoted by Alkali Metal Cations

AbstractAcidic H2O2 synthesis through electrocatalytic 2e− oxygen reduction presents a sustainable alternative to the energy‐intensive anthraquinone oxidation technology. Nevertheless, acidic H2O2 electrosynthesis suffers from low H2O2 Faradaic efficiencies primarily due to the competing reactions of 4e− oxygen reduction to H2O and hydrogen evolution in environments with high H+ concentrations. Here, we demonstrate the significant effect of alkali metal cations, acting as competing ions with H+, in promoting acidic H2O2 electrosynthesis at industrial‐level currents, resulting in an effective current densities of 50–421 mA cm−2 with 84–100 % Faradaic efficiency and a production rate of 856–7842 μmol cm−2 h−1 that far exceeds the performance observed in pure acidic electrolytes or low‐current electrolysis. Finite‐element simulations indicate that high interfacial pH near the electrode surface formed at high currents is crucial for activating the promotional effect of K+. In situ attenuated total reflection Fourier transform infrared spectroscopy and ab initio molecular dynamics simulations reveal the central role of alkali metal cations in stabilizing the key *OOH intermediate to suppress 4e− oxygen reduction through interacting with coordinated H2O.

The dissociation of H2O on the γ-U (110) and (100) surfaces: an ab initio study

The dissociation of H2O on γ-U (110) and γ-U (100) surfaces has been studied by using ab initio molecular dynamics simulations at an elevated temperature of 800 K. The simulation results show the dissociation of H2O into the OH group and H atom, which are finally adsorbed on the uranium surface. The dissociation results from electronic interactions between surface uranium 6d/5 f states and the s orbitals of H and the 2p orbitals of O. Additionally, the hybridization between the 6d orbital of surface uranium and the 2p orbital of oxygen plays a dominant role in dissociative adsorption. A significant charge transfer from the uranium surface to the O and H atoms is observed, indicating the formation of U–O and U–H chemical bonds. Specifically, for γ-U (110) surface, the most preferred site for OH is the 3-fold hollow site and H occupies the bridge site or the 3-fold hollow site. On the other hand, for γ-U (100) surface, OH prefers to adsorb on the bridge site and H occupies the 3-fold hollow site or the bridge site. Furthermore, when H2O is placed on the TOP site, its initial dissociation on the γ-U (110) surface is easier compared to the γ-U (100) surface.

Superparamagnetic nanofluid based on target-specific deep eutectic solvent for determination of multiple perfluoroalkyl substances in edible oils

Deep eutectic solvents (DESs) are recognized as sustainable mediums, and DES-related materials have been used for the detection of perfluoroalkyl substances (PFASs). However, such studies were usually limited to only one category of PFASs among the massive target PFASs compounds. Additionally, the selectivity of the related detection method still needs improvement. In this study, a convenient and effective method for the direct selective microextraction of multiple PFASs was developed based on a target-specific DES-based superparamagnetic nanofluid. Parameters such as DES compositions, amount of DES-based nanofluid, and microextraction time were systematically investigated to establish a straightforward, rapid, sensitive, and efficient green pretreatment method. Under optimal conditions, the method demonstrated high sensitivity, good precision, a detection limit of 0.04–8.71 ng kg−1, a spike recovery of 80.49–119.95%, and low matrix effects (<20%). The potential mechanism was elucidated by ab initio molecular dynamics (AIMD) simulations. The solvent system exhibited diverse interaction modes with analytes of varying types, including hydrogen bond acceptors (HBA)···PFASs, HBA···FAAs···hydrogen bond donors (HBD), and hetero-halogen interactions. Finally, this method was applied to the monitoring of 13 PFASs compounds in 17 edible oil samples, and targets were detected in the range of 0.05–10.04 ng kg−1.

Unveiling reversible hydrogen storage mechanism for the 2D penta-SiCN material

The promise of using 2D materials for hydrogen storage has broad prospects, ascribe to their significant specific surface area and lightweight properties. In this work, the hydrogen storage capability and reversible storage mechanism of 2D penta-SiCN material are investigated based on the first-principles computational method. Thermal stability of penta-SiCN is calculated by the ab-initio molecular dynamics (AIMD) simulation and root-mean-square displacement (RMSD) algorithm. It has been found that penta-SiCN is thermodynamically stable even after adsorbing hydrogen molecules. Taking into account the benchmarks of average and continuous adsorption energies of the adsorption systems, a pristine 2 × 2 × 1 penta-SiCN substrate has the ability to adsorb up to 26H2 molecules, which results in a maximum hydrogen storage capacity of 10.80 wt%. According to the semi-empirical calculation method that based on the thermodynamic analysis, the penta-SiCN adsorption system has a high reversible hydrogen storage capacity of 9.57 wt% within the adsorption and desorption application working conditions. The results proposed in this study demonstrates that penta-SiCN exhibits considerable promise for hydrogen storage with its substantial hydrogen storage capacity, exceptional reversibility, and eco-friendly characteristics.

The dual-transition-metal dichalcogenide monolayers anchored with Mn dimer: Promising electrocatalysts for efficient nitrogen reduction reaction

Due to its great efficiency, the electrocatalytic nitrogen reduction reaction (NRR) presents itself as a viable and eco-friendly substitute for the traditional Haber-Bosch ammonia production process. However, it is still a formidable task to find electrocatalysts with high activity and selectivity. In this study, a series of transition metals (TM = Ti–Ni, Zr–Mo, Ru–Pd, and Hf–Pt) anchored on 1T′-dual-transition-metal dichalcogenides (1T′-d-TMDs) monolayers (TM2@1T′-CrCoS4) were systematically investigated as electrocatalysts for NRR using first-principles calculations based on density functional theory. Based on a thorough examination of selectivity, high activity, and stability, Mn2@1T′-CrCoS4 and Co2@1T′-CrCoS4 demonstrate exceptional NRR performance. With a limiting potential of −0.11 V, Mn2@1T′-CrCoS4 stood out among them in terms of catalytic activity, favoring the enzymatic pathway. Furthermore, ab initio molecular dynamics (AIMD) simulations were used to assess the dynamic stability of Mn2@1T′-CrCoS4 and Co2@1T′-CrCoS4. To determine the source of increased activities, the density of states (DOS), charge density difference, and crystal orbital Hamilton population analysis were used. According to our research, the 1T′-d-TMDS is a viable substrate for the development of effective NRR catalysts and offers a platform for electrocatalyst experimentation.

Confinement driving mechanism of surface methoxy species formation in mordenite zeolite: An interplay of different molecular factors

Surface methoxy species (SMS) are key intermediates in methanol conversion within zeolites. We propose a reaction mechanism for SMS formation using methanol or dimethyl ether in mordenite zeolites, based on ab initio molecular dynamics (AIMD) simulations and validated by in situ experiments. Key factors such as adsorption, diffusion, distribution, and attacking modes of reactants were considered. The forward attacking mode of both methanol and dimethyl ether on the acid site is more feasible for SMS formation than the backward mode in the 8 member-ring of mordenite (MOR-8MR). For methanol, two end-to-end molecules in MOR-8MR promote SMS formation via a stepwise pathway, avoiding the rotation of protonated methanol, while two methanol molecules on different sides of acid site hinder SMS formation. Dimethyl ether, however, converts to SMS in MOR-8MR regardless of concentration and distribution. The kinetics align with in situ Fourier transform infrared experiments and are confirmed by two-dimensional correlation analysis of methanol dehydration.

Highly efficient photocatalytic performance of Z-scheme BTe/HfS2 heterostructure for H2O splitting

Constructing van der Waals (vdW) heterostructures is one of the effective strategies for developing highly efficient photocatalysts. In this study, we have designed a novel BTe/HfS2 heterostructure and systematically investigated its electronic properties and photocatalytic performance using first-principles calculations. The dynamic stability and thermodynamic stability of the heterostructure are verified through phonon spectrum simulations and ab initio molecular dynamics (AIMD) simulations, respectively, enhancing the likelihood of experimental synthesis. The bandgap of the BTe/HfS2 heterostructure is 0.12 eV, and the band edge positions satisfy the overall water splitting requirements for photocatalysts. The charge density difference, work function, Bader charge, and band alignment all confirm that the BTe/HfS2 heterostructure is a typical direct Z-scheme heterostructure, effectively facilitating the separation of photogenerated charge carriers and exhibiting strong redox capability. The solar-to-hydrogen (STH) efficiency of the BTe/HfS2 heterostructure reaches as high as 17.32 %. Moreover, the heterostructure exhibits strong light absorption capability, reaching a magnitude of 105. The carrier mobility of the BTe/HfS2 heterostructure surpasses that of two individual monolayer materials, with the hole mobility in the x-direction reaching an impressive 28357.15 cm2s-1V-1. Simultaneously, the Gibbs free energy indicates that the BTe/HfS2 heterostructure can undergo the hydrogen evolution reaction (HER) with only 0.19 eV of external potential at pH = 0. Moreover, at pH = 7, it can spontaneously convert H2O into O2. Therefore, the newly designed BTe/HfS2 heterostructure offers a new direction for practical applications of photocatalysts.