Ab Initio Molecular Dynamics Calculations Research Articles

Graph Theoretic Molecular Fragmentation for Multidimensional Potential Energy Surfaces Yield an Adaptive and General Transfer Machine Learning Protocol.

Over a series of publications we have introduced a graph-theoretic description for molecular fragmentation. Here, a system is divided into a set of nodes, or vertices, that are then connected through edges, faces, and higher-order simplexes to represent a collection of spatially overlapping and locally interacting subsystems. Each such subsystem is treated at two levels of electronic structure theory, and the result is used to construct many-body expansions that are then embedded within an ONIOM-scheme. These expansions converge rapidly with many-body order (or graphical rank) of subsystems and have been previously used for ab initio molecular dynamics (AIMD) calculations and for computing multidimensional potential energy surfaces. Specifically, in all these cases we have shown that CCSD and MP2 level AIMD trajectories and potential surfaces may be obtained at density functional theory cost. The approach has been demonstrated for gas-phase studies, for condensed phase electronic structure, and also for basis set extrapolation-based AIMD. Recently, this approach has also been used to derive new quantum-computing algorithms that enormously reduce the quantum circuit depth in a circuit-based computation of correlated electronic structure. In this publication, we introduce (a) a family of neural networks that act in parallel to represent, efficiently, the post-Hartree-Fock electronic structure energy contributions for all simplexes (fragments), and (b) a new k-means-based tessellation strategy to glean training data for high-dimensional molecular spaces and minimize the extent of training needed to construct this family of neural networks. The approach is particularly useful when coupled cluster accuracy is desired and when fragment sizes grow in order to capture nonlocal interactions accurately. The unique multidimensional k-means tessellation/clustering algorithm used to determine our training data for all fragments is shown to be extremely efficient and reduces the needed training to only 10% of data for all fragments to obtain accurate neural networks for each fragment. These fully connected dense neural networks are then used to extrapolate the potential energy surface for all molecular fragments, and these are then combined as per our graph-theoretic procedure to transfer the learning process to a full system energy for the entire AIMD trajectory at less than one-tenth the cost as compared to a regular fragmentation-based AIMD calculation.

N-based single and double transition metal V2N/CrVN monolayers as high capacity anode materials for Li-ion batteries

The electrochemical characteristics of N-based single and double transition metal V2N/CrVN monolayers were examined using density functional theory (DFT) approach. The ab-initio molecular dynamics (AIMD) calculations have demonstrated that both V2N and CrVN monolayers are thermally stable at 300 & 500 K. The multilayer adsorption of Li-ion on both lower and upper surfaces of V2N/CrVN leads to the specific capacity of 1040/1440 mAh g−1. Moreover, the energy diffusion barrier is found to be 0.034 and 0.030 eV for V2N and CrVN MXenes, respectively. This observation authenticates that the replacement of V-layer by Cr-atomic layer considerably reduces the energy barrier and boosts the cycling rate of the batteries. Also, the calculated average working voltage of V2N/CrVN monolayers comes out in the range of 0.20–0.54 V which implies their application as anode material in Li-ion batteries. Thus with the enhanced electrochemical properties, both monolayers offer alternative candidatures for anodes in futuristic Li-ion batteries.

An ab initio molecular dynamics investigation of the thermophysical properties of molten NaCl-MgCl[formula omitted

Molten salts have many applications in the nuclear and solar energy industries for thermal storage and heat transfer applications. However, there is a knowledge gap in molten salt thermophysical properties which hinders the technical readiness level of molten salt applications, especially in the nuclear industry. A common method of investigating new materials is through ab initio Molecular Dynamics (AIMD) simulations which is an effective tool to investigate structural and thermophysical properties at realistic temperatures. NaCl-MgCl2 is an inexpensive salt that is a good candidate for use as a heat transfer medium in solar power applications or in the secondary loop of a nuclear reactor. In this article, the thermophysical properties of NaCl-MgCl2 are computed via AIMD calculations to supplement the limited experimental studies in the literature. A wide range of compositions and temperatures for the pseudo-binary NaCl-MgCl2 were used to calculate the density, heat capacity, compressibility, enthalpy of mixing, and volumetric thermal expansion coefficient. AIMD is shown to accurately model the densities of molten NaCl-MgCl2 as there is good agreement with the available literature. This work observed a transition to a monotonic increase of the density with respect to MgCl2 composition occurring above 1100 K. The heat capacity values increase uniformly with respect to concentration of MgCl2 at a rate of 2.85 J/mol-K per 10 mol% of MgCl2. Select thermophysical properties are fit to a Redlich-Kister expansion for utilization in multiphysics simulations.

In situ spectroelectrochemical probing of CO redox landscape on copper single-crystal surfaces

Electrochemical reduction of CO(2) to value-added chemicals and fuels is a promising strategy to sustain pressing renewable energy demands and to address climate change issues. Direct observation of reaction intermediates during the CO(2) reduction reaction will contribute to mechanistic understandings and thus promote the design of catalysts with the desired activity, selectivity, and stability. Herein, we combined in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy and ab initio molecular dynamics calculations to investigate the CORR process on Cu single-crystal surfaces in various electrolytes. Competing redox pathways and coexistent intermediates of CO adsorption (*COatop and *CObridge), dimerization (protonated dimer *HOCCOH and its dehydrated *CCO), oxidation (*CO2- and *CO32-), and hydrogenation (*CHO), as well as Cu-Oad/Cu-OHad species at Cu-electrolyte interfaces, were simultaneously identified using in situ spectroscopy and further confirmed with isotope-labeling experiments. With AIMD simulations, we report accurate vibrational frequency assignments of these intermediates based on the calculated vibrational density of states and reveal the corresponding species in the electrochemical CO redox landscape on Cu surfaces. Our findings provide direct insights into key intermediates during the CO(2)RR and offer a full-spectroscopic tool (40-4,000 cm-1) for future mechanistic studies.

Hydrated Anions: From Clusters to Bulk Solution with Quasi-Chemical Theory.

ConspectusThe interactions of hydrated ions with molecular and macromolecular solution and interface partners are strong on a chemical energy scale. Here, we recount the foremost ab initio theory for the evaluation of the hydration free energies of ions, namely, quasi-chemical theory (QCT). We focus on anions, particularly halides but also the hydroxide anion, because they have been outstanding challenges for all theories. For example, this work supports understanding the high selectivity for F– over Cl– in fluoride-selective ion channels despite the identical charge and the size similarity of these ions. QCT is built by the identification of inner-shell clusters, separate treatment of those clusters, and then the integration of those results into the broader-scale solution environment. Recent work has focused on a close comparison with mass-spectrometric measurements of ion-hydration equilibria. We delineate how ab initio molecular dynamics (AIMD) calculations on ion-hydration clusters, elementary statistical thermodynamics, and electronic structure calculations on cluster structures sampled from the AIMD calculations obtain just the free energies extracted from the cluster experiments. That theory–experiment comparison has not been attempted before the work discussed here, but the agreement is excellent with moderate computational effort. This agreement reinforces both theory and experiment and provides a numerically accurate inner-shell contribution to QCT. The inner-shell complexes involving heavier halides display strikingly asymmetric hydration clusters. Asymmetric hydration structures can be problematic for the evaluation of the QCT outer-shell contribution with the polarizable continuum model (PCM). Nevertheless, QCT provides a favorable setting for the exploitation of PCM when the inner-shell material shields the ion from the outer solution environment. For the more asymmetrically hydrated, and thus less effectively shielded, heavier halide ions clustered with waters, the PCM is less satisfactory. We therefore investigate an inverse procedure in which the inner-shell structures are sampled from readily available AIMD calculations on the bulk solutions. This inverse procedure is a remarkable improvement; our final results are in close agreement with a standard tabulation of hydration free energies, and the final composite results are independent of the coordination number on the chemical energy scale of relevance, as they should be. Finally, a comparison of anion hydration structure in clusters and bulk solutions from AIMD simulations emphasize some differences: the asymmetries of bulk solution inner-shell structures are moderated compared with clusters but are still present, and inner hydration shells fill to slightly higher average coordination numbers in bulk solution than in clusters.

Substitution Effects on the Reactivity and Thermostability of Five-Membered Ring Fluorides

Recently, five-membered ring fluorides (c-C5Fs) have been significantly desirable in green chlorofluorocarbon substitutes due to their practically flexible application in various fields and environmental friendliness. Detailed knowledge regarding different substitution effects on their environmental properties and thermal stability is very limited due to their high-cost experiments. Here, comprehensive density functional theory and ab initio molecular dynamics calculations were performed to explore the relative electrophilic and nucleophilic reactivity and thermostability of c-C5F chemicals. The electronic properties induced by substitution effects of c-C5Fs were first explored. The environmental friendliness of c-C5Fs including 1,1,2,2,3,3-hexafluorocyclopentane (F6A), 1,1,2,2,3,3,4-heptafluorocyclopentane (F7A), cis-1,1,2,2,3,3,4,5-octafluorocyclopentane (F8A), 3,3,4,4,5,5-hexafluorocyclopentene (F6E), 1,3,3,4,4,5,5-heptafluorocyclopentene (F7E), octafluorocyclopentene (F8E), 1-chloro-3,3,4,4,5,5-hexafluorocyclopent-1-ene (F6-1), and 1-chloro-2,3,3,4,4,5,5-heptafluorocyclopent-1-ene (F7-1) was validly confirmed. Besides, their thermal stabilities at 600 K temperature were concluded due to their flexible carbon skeletons, where both in-plane stability and slight aromaticity of F6E were in peculiar found to contribute substantially. We also would like to stress the future application of F6-1 due to its significant out-plane stability. This study may pave the way for the development of chlorofluorocarbon substitutes.

Observation of intermolecular Coulombic decay and shake-up satellites in liquid ammonia.

We report the first nitrogen 1s Auger–Meitner electron spectrum from a liquid ammonia microjet at a temperature of ∼223 K (–50 °C) and compare it with the simultaneously measured spectrum for gas-phase ammonia. The spectra from both phases are interpreted with the assistance of high-level electronic structure and ab initio molecular dynamics calculations. In addition to the regular Auger–Meitner-electron features, we observe electron emission at kinetic energies of 374–388 eV, above the leading Auger–Meitner peak (3a12). Based on the electronic structure calculations, we assign this peak to a shake-up satellite in the gas phase, i.e., Auger–Meitner emission from an intermediate state with additional valence excitation present. The high-energy contribution is significantly enhanced in the liquid phase. We consider various mechanisms contributing to this feature. First, in analogy with other hydrogen-bonded liquids (noticeably water), the high-energy signal may be a signature for an ultrafast proton transfer taking place before the electronic decay (proton transfer mediated charge separation). The ab initio dynamical calculations show, however, that such a process is much slower than electronic decay and is, thus, very unlikely. Next, we consider a non-local version of the Auger–Meitner decay, the Intermolecular Coulombic Decay. The electronic structure calculations support an important contribution of this purely electronic mechanism. Finally, we discuss a non-local enhancement of the shake-up processes.

Predicted Pressure-Induced High-Energy-Density Iron Pentazolate Salts

Metal-pentazolate compounds as candidates for novel high-energy-density materials have attracted extensive attention in recent years. However, dehydrated pentazolate salts of transition metal iron are rarely reported. We predict two new iron pentazolate salts Fdd2-FeN10 and (No.1)-FeN10 using a constrained crystal search method based on first-principles calculations. We propose that the stable Fdd2-FeN10 crystal may be synthesized from FeN and N2 above 20 GPa, and its formation enthalpy is lower than the reported iron pentazolate salt (marked as (No.2)-FeN10). Crystal (No.1)-FeN10 is composed of iron bispentazole molecules. Formation enthalpy, phonon spectrum and ab initio molecular dynamics calculations are performed to show their thermodynamic, mechanical and dynamic properties. Moreover, the high energy density (3.709 kJ/g, 6.349 kJ/g) and good explosive performance indicate their potential applications as high-energy-density materials.

Ab initio molecular dynamics free energy study of enhanced copper (II) dimerization on mineral surfaces

Understanding the adsorption of isolated metal cations from water on to mineral surfaces is critical for toxic waste retention and cleanup in the environment. Heterogeneous nucleation of metal oxyhydroxides and other minerals on material surfaces is key to crystal growth and dissolution. The link connecting these two areas, namely cation dimerization and polymerization, is far less understood. In this work we apply ab initio molecular dynamics calculations to examine the coordination structure of hydroxide-bridged Cu(II) dimers, and the free energy changes associated with Cu(II) dimerization on silica surfaces. The dimer dissociation pathway involves sequential breaking of two Cu2+-OH− bonds, yielding three local minima in the free energy profiles associated with 0-2 OH− bridges between the metal cations, and requires the design of a (to our knowledge) novel reaction coordinate for the simulations. Cu(II) adsorbed on silica surfaces are found to exhibit stronger tendency towards dimerization than when residing in water. Cluster-plus-implicit-solvent methods yield incorrect trends if OH− hydration is not correctly depicted. The predicted free energy landscapes are consistent with fast equilibrium times (seconds) among adsorbed structures, and favor Cu2+ dimer formation on silica surfaces over monomer adsorption.

Thermal stability of the magnetic moment in amorphous carbon thin film - An experimental and ab-initio study

The effect of vacuum annealing on the microstructure and its consequence on the thermal stability of magnetic moment in amorphous carbon (a-C) thin film is studied. The magnetic a-C thin film of thickness 8 nm is vacuum annealed for 2 h at 523 K and 923 K. Microstructural and chemical characterization using Raman spectroscopy and x-ray photoelectron spectroscopy, respectively, reveals that with increasing annealing temperature, the sp2 fraction in the film increases. The magnetic measurement carried out at room temperature (RT) using SQUID-VSM reveals a weak ferromagnetic signal in the film due to the interaction between the unpaired sp2 sites, which prevails till 923 K. In the as-deposited sample, an isolated sp2 atom surrounded by sp3 atom results in the paramagnetic contribution, and an sp2-sp2 atom with twisted π-orbitals results in weak ferromagnetic coupling. Compared with the as-deposited case, initially, the saturation magnetization increases when the sample is annealed at 523 K and later decreases when annealed at 923 K. Subsequently, the ab-initio molecular dynamics calculation predicts that due to the increase in sp2 fraction, the net magnetization of the system increases from 300 K to 523 K. π-Orbital Axis Vector (POAV) analysis shows that further annealing to 923 K enhances π-orbital overlapping, which leads to the annihilation of moments sites. The present study differentiates between the two structures that contribute to the magnetism in a-C in terms of their thermal stability. Our simulation indicates that the twisted π-orbitals structure is thermodynamically more stable than the structure where sp3 surrounds sp2 hybridized atom.

The effect of water on the outer core transport properties

Recent studies suggest that incorporation of water in the core during core-mantle differentiation is highly plausible; this could significantly influence outer-core transport properties, which has yet to be rigorously studied. We performed ab initio molecular dynamics calculations to investigate the effect of water on the transport properties of liquid iron. We find, at the thermodynamic limit, that the self-diffusion coefficients for Fe are remarkably larger than previously reported values, with and without water. Both the bulk and shear viscosities are of the order of 10−3 Pa·s for the outer core. Water, in the form of H or H2O, can enhance the diffusion of Fe moderately and cause a reduction in both the shear and bulk viscosities, giving rise to an inviscid outer core. The fast liquid Fe dynamics is consistent with the origin and stability of a chemically stratified layer at the topmost outer core. By considering the density jump at the inner-core boundary, we determine that the H content cannot exceed 0.3 wt% in the outer core.

Theoretical Studies of a Silica Functionalized Acrylamide for Calcium Scale Inhibition

The calcium carbonate (CaCO3) scale is one of the most common oilfield scales and oil and gas production bane. CaCO3 scale can lead to a sudden halt in production or, worst-case scenario, accidents; therefore, CaCO3 scale formation prevention is essential for the oil and gas industry. Scale inhibitors are chemicals that can mitigate this problem. We used two popular theoretical techniques in this study: Density Functional Theory (DFT) and Ab Initio Molecular Dynamics (AIMD). The objective was to investigate the inhibitory abilities of mixed oligomers, specifically acrylamide functionalized silica (AM-Silica). DFT studies indicate that Ca2+ does not bind readily to acryl acid and acrylamide; however, it has a good binding affinity with PAM and Silica functionalized PAM. The highest binding affinity occurs in the silica region and not the –CONH functional groups. AIMD calculations corroborate the DFT studies, as observed from the MD trajectory that Ca2+ binds to PAM-Silica by forming bonds with silicon; however, Ca2+ initially forms a bond with silicon in the presence of water molecules. This bonding does not last long, and it subsequently bonds with the oxygen atoms present in the water molecule. PAM-Silica is a suitable calcium scale inhibitor because of its high binding affinity with Ca2+. Theoretical studies (DFT and AIMD) have provided atomic insights on how AM-Silica could be used as an efficient scale inhibitor.

Formation of Metallic Ag on AgBr by Femtosecond Laser Irradiation

Laser irradiation of materials induces changes in their structure and functional properties. In this work, lattice heating and electronic excitation on silver bromide (AgBr), provoked by femtosecond laser irradiation, have been investigated by finite-temperature density functional theory and ab initio molecular dynamics calculations by using the two-temperature model. According to our results, the electronic temperature of 0.25 eV is enough to excite the electrons from the valence to the conduction band, whereas 1.00 eV changes the structural properties of the irradiated AgBr material. Charge density simulations also show that an Ag clustering process and the formation of Br3− complexes take place when the electronic temperature reaches 2.00 eV and 5.00 eV, respectively. The present results can be used to obtain coherent control of the extreme nonequilibrium conditions due to femtosecond laser irradiation for designing new functional materials.

Rearrangement of dicarboranyl methyl cation to icosahedral C3 B9 H12 + : An ab initio dynamics view.

Closo-carborane anions are prominent, whereas the cations of the same are less abundant in the literature. As these ions have similar size and are weakly coordinating, the ionic liquids of these two ions could have important applications in many areas of chemistry. In view of limited number of polyhedral carborane cations available, we revisited the rearrangement of dicarboranyl methyl cation (7-CH2 7,9-nido-C2 B9 H10 + ) using ab initio molecular dynamics calculations with metadynamics. Our simulations confirmed the concerted mechanism of the rearrangement. We believe this work will resume the interest in its synthesis and carborane cations in general.

Effect of non-magnetic doping on magnetic state and Li/Na adsorption and diffusion of black phosphorene

Black phosphorene (BP) have aroused great concern because of its great potential for the application in nanoelectronic devices and high-performance anode materials for alkali metal ion batteries (AIBs). However, the absence of magnetism for an ideal BP limits its wide application in spintronic devices which is one of the important nanoelectronic devices, and its application as a high-performance anode material for AIBs is still to be explored. In this paper, we adopt first-principles calculations to explore the effects of B, C, N, O, F, Al, Si and S atom doping on the magnetic state of monolayer BP and Li or Na atom adsorption and diffusion on the BP. Additionally, the thermal stability of the doped BP systems at room temperature is revealed by the ab initio molecular-dynamics calculations. Our calculated results indicate that O and S doping can make the doped BP become a magnetic semiconductor, C and Si doping makes the doped BP be metallic, and B, N, F and Al doping preserves semiconductor property. Moreover, little structural changes and significant decreases of diffusion barriers in armchair direction and slight increases of diffusion barriers in zigzag direction make B-doped BP beneficial as an anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). It reveals that S-doping is suitable for improving the performance of SIBs rather than LIBs. Interestingly, it is found that magnetic states of O- and S-doped BP disappear when Li or Na atoms adsorb on them, whereas Li or Na adsorption on B- and Al-doped BP induces magnetic states of these systems. The analyses indicate that the distinct electron transfer between the dopant atom, adatom and neighboring P atoms, and specific electron configuration of dopant atoms cause the magnetism of the systems. Our results suggest that selecting appropriate composition to dope can effectively manipulate magnetic state and improve Li/Na adsorption and diffusion on the BP. These results may inspire further theoretical and experimental exploration on doped two-dimensional (2D) materials in spintronics and doped 2D promising anode materials for high-performance metal ion batteries.

ZnC3-2D a new material for hydrogen reversible storage predicted by first-principles calculations

In order to improve the transport, electronics and storage properties of graphene layers, we have constructed compact structures with graphene sheets. With the Use of the density functional theory (DFT) and ab-initio molecular dynamics (AIMD) calculations including van der Waals interactions, the structural stability and hydrogen storage properties of the neat ZnC3 monolayer have been systematically investigated, the adsorption of H2 molecules on ZnC3 shows good results. A high binding energy up to 0.3169 eV with 3.30 Å as equilibrium distance. A low activation energy allows the molecule to migrate on the surface so easily up to 0.022 eV. The investigation revealed a high gravimetric (GC) and volumetric (Vc) capacities up to 7.73 wt% and 98.44 g/l as a new 2D material for hydrogen storage. The hydrogenation/dehydrogenation (desorption) temperature is expected to be 215.55 K. The desorption temperature (TD) proved to be significantly greater as compared to the critical point of hydrogen (33 K). Furthermore, the TD calculations were confirmed with AIMD simulations of the adsorption of 17 H2 molecule on ZnC3. Thus, the monolayer ZnC3 could function as a reversible hydrogen storage substrate under feasible conditions.

Degradation of Per- and Polyfluoroalkyl Substances with Hydrated Electrons: A New Mechanism from First-Principles Calculations.

Per- and polyfluoroalkyl substances (PFASs) are synthetic contaminants found in drinking groundwater sources and a wide variety of consumer products. Because of their adverse environmental and human health effects, remediation of these persistent compounds has attracted significant recent attention. To gain mechanistic insight into their remediation, we present the first ab initio study of PFAS degradation via hydrated electrons─a configuration that has not been correctly considered in previous computational studies up to this point. To capture these complex dynamical effects, we harness ab initio molecular dynamics (AIMD) simulations to probe the reactivities of perfluorooctanoic (PFOA) and perfluorooctane sulfonic acid (PFOS) with hydrated electrons in explicit water. We complement our AIMD calculations with advanced metadynamics sampling techniques to compute free energy profiles and detailed statistical analyses of PFOA/PFOS dynamics. Although our calculations show that the activation barrier for C-F bond dissociation in PFOS is three times larger than that in PFOA, all the computed free energy barriers are still relatively low, resulting in a diffusion-limited process. We discuss our results in the context of recent studies on PFAS degradation with hydrated electrons to give insight into the most efficient remediation strategies for these contaminants. Most importantly, we show that the degradation of PFASs with hydrated electrons is markedly different from that with excess electrons/charges, a common (but largely incomplete) approach used in several earlier computational studies.

Mo2CS2-MXene supported single-atom catalysts for efficient and selective CO2 electrochemical reduction

Single-atom catalysts (SACs) recently attracted considerable attention in heterogeneous catalysis, owing to high atom-utilization and unique properties. In this paper, we investigated geometry, electronic structure, stabilities, catalytic activity, and selectivity of the various TM@Mo2CS2 (TM = Fe, Co, Ni, Cu, Ru. Rh, Pd, Ag, Os, Ir, Pt, and Au) anchored SACs for CO2 electrochemical reduction using periodic density functional theory and ab-initio molecular dynamics calculations. The single metal atoms tend to occupy the Mo-top site on the Mo2CS2 surface. Possible different reaction pathways to produce various C1 products such as CO, HCOOH, HCHO, CH3OH, and CH4 have been investigated for Fe, Co, Ni, and Ru supported SACs. Among the SACs investigated, Fe, Co, and Ru supported by Mo2CS2 catalysts selectively produce CH4, whereas Ru@Mo2CS2 has the lowest overpotential of 0.24 V. Ni primarily produces HCOOH with an overpotential is 0.37 V. Therefore, this research demonstrated the significant potential of Mo2CS2 surface for a single-atom catalyst for selective CO2 reduction and other electrochemical applications.

Temperature and pressure driven spin transitions and piezochromism in a Mn-based hybrid perovskite

Hybrid perovskites have been at the forefront of condensed matter research particularly in context of device applications primarily in relation to applications in the field of solar cells. In this article, we demonstrate that several new functionalities may be added to the arsenal of hybrid perovskites, in terms of external stimuli driven spin transitions as well as piezochromism. As an example, we study Dimethylammonium Manganese Formate (DMAMnF), a hybrid perovskite investigated quite extensively experimentally. We show by employing first principles DFT+U calculations with the aid of ab initio molecular dynamics calculations that DMAMnF shows temperature and pressure driven spin transitions, from a low spin $S=1/2$ to a high spin $S=5/2$ state. This transition is accompanied by a hysteresis, and we find that this hysteresis and the transition temperature are quite close to room temperature, which is desirable for device applications particularly in memory, display, and switching devices. The operating pressure is a few GPa, which is accessible in standard laboratory settings. We find that the cooperative behaviour showing up as hysteresis accompanying the transition is driven primarily by elastic interactions, assisted by magnetic superexchange between Mn atoms. Last but not least we demonstrate that the spin transition is associated with piezochromism which could also be important for applications.

SiC Monolayers as Promising Substrates for the Development of Highly Stable Palladium Single Atom Catalysts: A Density Functional Theory Study

Single-atom catalysts have been touted as highly efficient catalysts, but the catalytic single-atom sites are unstable and tend to aggregate into nanoparticles during chemical reactions. In this study, we show that SiC monolayers are promising substrates for the development of highly stable single-atom catalysts (Pd1 /SiC) within the density functional theory. In presence of a Si-vacancy, the diffusion barrier energy of a Pd1 atom embedded in the SiC monolayer is substantially enhanced from 2.3 to 7.8 eV, which is much higher than the reported diffusion barrier energies of graphene, boron nitride and defective MgO of the same catalytic system. Ab initio molecular dynamic calculations at 500 K also confirm the enhanced stability of Pd1 /SiC monolayer (Si-vacancy) such that the Pd1 atom remains embedded in the vacancy. Additionally, the Pd1 /SiC monolayer (Si-vacancy) catalysts show a ∼34 % reduction of activation barrier energy for CO oxidation as compared to pristine catalysts. This work implies that nanostructured SiC materials are promising substrates for the synthesis of highly stable single-atom catalysts.