Exploring phononic properties of two-dimensional materials using machine learning interatomic potentials

Accurate examination of electricity generation stemming from higher‐order deformation (flexoelectricity) in 2D layered materials is a highly challenging task to be investigated with either conventional computational or experimental tools. To address this challenge herein an innovative and computationally efficient approach on the basis of density functional theory (DFT) and machine‐learning interatomic potentials (MLIPs) with incorporated long‐range interactions to accurately investigate the flexoelectric energy conversion in 2D van der Waals (vdW) bilayers is proposed. In this approach, short‐range interactions are accurately defined using the moment tensor potentials trained over computationally inexpensive DFT‐based datasets. The long‐range electrostatic (charge and dipole) and vdW interaction parameters are calibrated from DFT simulations. Elaborated comparison of mechanical and piezoelectric properties extracted from the herein proposed approach with available data confirms the accuracy of the devised computational strategy. It is shown that the bilayer transition metal dichalcogenides can show a flexoelectric coefficient 2–7 times larger than their monolayer counterparts. Noticeably, this enhancement reaches up to 20 times for Janus diamane and fluorinated boron‐nitrogen derivatives of diamane bilayers. The presented results improve the understanding of the flexoelectric effect in vdW heterostructures and moreover the proposed MLIP‐based methodology offers a robust tool to improve the design of novel energy harvesting devices.

In this paper, we device stress-diffusion full coupling multiscale analysis method for battery electrode simulation. In proposed method, the diffusive and mechanical properties of electrode material depend on Li concentration are estimated using density function theory(DFT) simulation. Then, stress-diffusion full coupling continuum formulation based on finite element method(FEM) is constructed with the diffusive and mechanical properties calculated from DFT simulation. Finally, silicon nanowire anode charge and discharge simulations are performed using the proposed method. Through numerical examples, the stress-diffusion full coupling method shows more resonable results than previous one way continuum analysis.

Machine learning (ML) interatomic potentials (ML-IAPs) are generated for alkane and polyene hydrocarbons using on-the-fly adaptive sampling and a sparse Gaussian process regression (SGPR) algorithm. The ML model is generated based on the PBE+D3 level of density functional theory (DFT) with molecular dynamics (MD) for small alkane and polyene molecules. Intermolecular interactions are also trained with clusters and condensed phases of small molecules. It shows excellent transferability to long alkanes and closely describes the ab inito potential energy surface for polyenes. Simulation of liquid ethane also shows reasonable agreement with experimental reports. This is a promising initiative toward a universal ab initio quality force-field for hydrocarbons and organic molecules.

The fundamental knowledge of the interaction between biomolecules and mineral surfaces is of utmost importance to drive new technological advancements, particularly for condensation, aggregation, catalysis and exchange of biomolecules. The mineral surface can be used in several fields and applications, for instance in biotechnology, environmental science and remediation, soil science, agro-food and related technology. This kind of knowledge may also provide several suggestions and have implications also for the prebiotic chemistry field, namely the study of the abiotic physicochemical steps that could have led to the 'creation' of the first known living organism. Nowadays, this kind of information at the micro and nanometric scale can be explored with several experimental and theoretical techniques and, among them, atomic force microscopy (AFM)-related methods and density functional theory (DFT) are particularly suited to investigate adsorption processes at single molecule level. In the present work, the specific interaction at the atomic scale between a small peptide (di-glycine) and the (001) surface of clinochlore, a mineral presenting alternately stacked talc-like layers (hydrophilic) and brucite-like sheets (hydrophobic), was characterized by means of a cross-correlated approach combining AFM and DFT simulations. The experiments evidenced the preferential adsorption of di-glycine onto the hydrophobic brucite-like sheet of the mineral, with the observed molecules organized as dot-like (single-molecules), agglomerates, filament-like and network structures by the surface, whereas only very few peptides were imaged onto the hydrophilic talc-like layer. From the theoretical analysis, the most stable conformation of the di-glycine peptide adsorbed on the mineral surface was calculated, and the binding energy analysis of the specific interaction of the molecule, depending on the local chemistry of the substrate, provided fundamental information to interpret end explain the experimental evidence. LAY DESCRIPTION: The present work aims at extending the knowledge of the biomolecules/minerals interaction world. The fundamental knowledge of the interaction between biomolecules and mineral surfaces is of utmost importance to drive the development of new technological advancements, particularly for condensation, aggregation, catalysis and exchange of biomolecules. The mineral surface can be used as substrate in several fields and applications, for instance in biotechnology, environmental science and remediation, soil science, agro-food and related technology. This kind of research may also provide several suggestions and have implications also for the prebiotic chemistry field, namely the study of the abiotic physicochemical steps that could have led to the "creation" of the first known living organism. Nowadays, this kind of research at the micro and nanometric scale can be performed with several experimental techniques and, among them, scanning probe microscopy-related methods are particularly suited to investigate surface adsorption processes at single molecule level. In the present work, the focus is on the specific interaction at the atomic scale between a small peptide (di-glycine) and the surface of clinochlore (a diffuse clay mineral). Clinochlore is a mineral belonging to the phyllosilicate, formed by alternately stacked hydrophilic talc-like layers [chemical formula Mg3 Si4 O10 (OH)2 ] and hydrophobic brucite-like sheets [magnesium hydroxide, Mg(OH)2 ]. Since these two kind of layered structures are held together by weak (van der Waals) forces, the mineral can be easily cleaved along the [001] crystallographic direction (the stacking direction) and the resulting (001) clinochlore surface may presents at the nanoscale some remainders of one layer (brucite-like or talc-like) on the other. This means that this mineral exposes to the environment two different type of surfaces, one hydrophilic and one hydrophobic, which can selectively interact with (adsorb) different type of molecules at the nanoscale. Clinochlore is also one of the 420 mineral species that were likely present on Earth at the time of life's origins, thus it could have played a fundamental role in prebiotic chemistry. In this study, the interaction between di-glycine and clinochlore was characterized by means of both atomic force microscopy (AFM) at the nanometric scale and density functional theory (DFT) simulations, correlating the results of the two methods (cross-correlation approach). The experiments evidenced the preferential adsorption of di-glycine onto the hydrophobic brucite-like sheet of the mineral, with the observed molecules organized as dot-like (single-molecules) structures, agglomerates, filaments and networks by the surface, whereas only very few peptides were imaged onto the hydrophilic talc-like layer. From the theoretical analysis, the most stable conformation of the di-glycine adsorbed on the mineral surface was calculated, and the binding energy analysis of the specific interaction of the molecule, depending on the local chemistry of the substrate, provided fundamental information to interpret end explain the experimental evidence.

Understanding the mechanical properties of metal–organic frameworks (MOFs) is essential to the fundamental advancement and practical implementations of porous materials. Recent computational and experimental efforts have revealed correlations between mechanical properties and pore size, topology, and defect density. These results demonstrate the important role of the organic linker in the response of these materials to physical stresses. However, the impact of the coordination bond between the inorganic node and organic linker on the mechanical stability of MOFs has not been thoroughly studied. Here, we isolate the role of this node–linker coordination bond to systematically study the effect it plays in the compression of a series of isostructural MOFs, M-UiO-66 (M = Zr, Hf, or Ce). The bulk modulus (i.e. the resistance to compression under hydrostatic pressure) of each MOF is determined by in situ diamond anvil cell (DAC) powder X-ray diffraction measurements and density functional theory (DFT) simulations. These experiments reveal distinctive behavior of Ce-UiO-66 in response to pressures under one GPa. In situ DAC Raman spectroscopy and DFT calculations support the observed differences in compressibility between Zr-UiO-66 and the Ce- analogue. Monitoring changes in bond lengths as a function of pressure through DFT simulations provides a clear picture of those which shorten more drastically under pressure and those which resist compression. This study demonstrates that changes to the node–linker bond can have significant ramifications on the mechanical properties of MOFs.

Tungsten carbide (WC) is an established model electrocatalyst for the hydrogen evolution reaction (HER) in aqueous solutions. In spite of extensive interest in and work on this material, a systematic atomistic understanding of the combined role of faceting and heteroatom doping for hydrogen evolution on WC electrocatalysts in aqueous solution is not available. To fill this knowledge gap, here we explore the interplay of these parameters for the electrocatalytic performance of WC by means of density functional theory (DFT) simulations. In our simulations, we explicitly account for solvent (water) effects and related electrochemical potential-dependent oxygen or hydroxyl (co)adsorption on the WC surfaces as determined by the analysis of surface Pourbaix diagrams. Among the several low-index WC surfaces screened, the DFT simulations indicate that the W-terminated (−100) and (111) surfaces of WC show comparable exchange currents of 3.908 and 0.133 mA/cm2, respectively. The simulations also suggest that V or N doping can substantially increase the HER activity of some WC surfaces to levels comparable to commercial Pt/C electrocatalysts, with current densities as large as 10.555, 1.730, and 0.636 mA/cm2 for the V-doped W-terminated (001), V-doped (101), and N-doped (101) WC surfaces, respectively. The improved HER activities are rationalized in terms of the d-band or p-band center, which are both shown to be related to the capability of tuning the hydrogen adsorption, and thence the HER performance. The calculated strong dependence of the HER activity on the presence of the electrochemical adsorption of oxygen and hydroxyls reiterates the importance of modeling realistic electrochemical conditions for WC pristine or doped surfaces. We expect the DFT results presented to provide timely and original guidelines for further theoretical and experimental studies of HER activity on WC-related electrocatalysts.

Absorbed oxygen plays a key role in gas sensing process of ZnO nanomaterials. In this work, the transformation of absorbed oxygen on ZnO (101̅0) and its effects on gas sensing properties to ethanol are studied by a novel thermal pulse method and density functional theory (DFT) simulation. Thermal pulse results reveal that the absorbed O2 molecule dissociates into two individual oxygen adatoms by extracting electrons from ZnO surface layers when temperature is above 443 K. The temperature at which absorbed O2 molecule begins to dissociate is the lowest working temperature for gas sensing. DFT simulation demonstrates the dissociation process of O2 at ZnO (101̅0) surface, and the activation energy (Ea) of dissociation is calculated to be 351.71 kJ/mol, which suggests that the absorbed O2 molecule is not likely to dissociate at room temperature. The reactions between ethanol and absorbed O2 molecule, as well as reactions between ethanol and O adatom, are also simulated. The results indicate that ethanol cannot react with absorbed O2 molecule, while it can be oxidized by O adatom to acetaldehyde and then to acetic acid spontaneously. Mulliken charge analysis suggests electrons extracted by O adatom return to ZnO after the oxidation of ethanol.

Perfluorinated C8-(PerfluoroC8) and bidentate anchored C8-(BDC8)-modified silica hydride stationary phases have been employed for the isocratic separation of homologous phenylalkanols and phenylalkylamines differing in their n-alkyl chain length, using aqueous-acetonitrile (ACN) mobile phases of different ACN contents from 10 to 90% (v/v) in 10% increments. These analytes showed reversed-phase (RP) retention behaviour with mobile phases of <40% (v/v) ACN content with both stationary phases but with the BDC8 stationary phase providing longer retention. The PerfluoroC8, but not the BDC8, stationary phase also exhibited significant retention of these analytes under conditions typical of an aqueous normal phase (ANP) mode (i.e. with mobile phases of >80% (v/v) ACN content), with the analytes exhibiting overall U-shape retention dependencies on the ACN content of the mobile phase. Further, these stationary phases showed differences in their selectivity behaviour with regard to the n-alkyl chain lengths of the different analytes. These observations could not be explained in terms of pKa, log P, molecular mass or linear solvation energy concepts. However, density functional theory (DFT) simulations provided a possible explanation for the observed selectivity trends, namely differences in the molecular geometries and structural organisation of the immobilised ligands of these two stationary phases under different solvational conditions. For mobile phase conditions favouring the RP mode, these DFT simulations revealed that interactions between adjacent BDC8 ligands occur, leading to a stationary phase with a more hydrophobic surface. Moreover, under mobile phase conditions favouring retention of the analytes in an ANP mode, these interactions of the bidentate-anchored C8 ligands resulted in hindered analyte access to potential ANP binding sites on the BDC8 stationary phase surface. With the PerfluoroC8 stationary phase, the DFT simulations revealed strong repulsion of individual perfluoroC8 ligand chains, with the perfluoroC8 ligands of this stationary phase existing in a more open brush-like state (and with a less hydrophobic surface) compared to the BDC8 ligands. These DFT simulation results anticipated the chromatographic findings that the phenylalkanols and phenylalkylamines had reduced retention in the RP mode with the PerfluoroC8 stationary phase. Moreover, the more open ligand structure of the PerfluoroC8 stationary phase enabled greater accessibility of the analytes to water solvated binding sites on the stationary phase surface under mobile phase conditions favouring an ANP retention mode, leading to retention of the analytes, particularly the smaller phenylalkylamines, via hydrogen bonding and electrostatic effects.

Degradation of caffeic acid by dielectric barrier discharge plasma combined with Ce doped CoOOH catalyst

Activated carbon adsorbent derived from waste biomass, “Croton caudatus” for efficient removal of 2-chlorophenol from aqueous solution: Kinetics, isotherm, thermodynamics and DFT simulation

This research investigated the oxidation of trichloroethene (TCE) at boron-doped diamond film electrodes. Flow-through experiments in gastight reactors were performed to determine trichloroethene oxidation products, and rotating disk electrode (RDE) experiments were used to determine TCE oxidation kinetics. RDE experiments were performed over a range in current densities and temperatures in order to elucidate the rate-limiting mechanisms for TCE oxidation. Density functional theory (DFT) simulations were used to investigate the activation barriers for oxidation by direct electron transfer and hydroxyl radicals. Oxidation of TCE produced formate, carbon dioxide, chlorate, and chloride. DFT simulations, experimentally measured apparent activation energies, and linear sweep voltammetry scans indicated that TCE oxidation occurred via direct electron transfer at electrode potentials <2.0 V/SHE, while at higher electrode potentials TCE oxidation also occurred via hydroxyl radicals produced from water oxidation.

Mechanistic study of the production of ethylene glycol diacetate as a byproduct of the ethylene vapor phase process for vinyl acetate on PdAu(100) surface

In recent decades, the concentration of dissolved organic matter (DOM) in aquatic ecosystems has gradually increased, leading to water pollution problems. Understanding the interfacial chemical processes of DOM on natural minerals is important to the exploration of high-efficiency absorbents. However, studying DOM chemical processes and adsorption mechanisms are still challenging due to the complex DOM structure and environmental system. Hence, we characterized the microstructure changes after the formation of amorphous calcium phosphate (ACP) at the interface of montmorillonite (Mt) minerals in a simulated environment system. Combined with atomic force microscopy and density functional theory (DFT) simulation, the mechanism of interfacial interaction between Mt-ACP and DOM was characterized at the molecular level. Moreover, we further evaluated the adsorption behavior of Mt-ACP as a potential adsorbent for organic matter. The comprehensive investigation of humic acid adsorption, intermolecular force, and DFT simulation is conducive to our understanding of the interfacial interaction mechanism between organic matter and noncrystalline minerals in aquatic environments and provides new perspectives on the application of clay-based mineral materials in pollutant removal under exposure from DOM.

Nanoscale oligopeptide adsorption behaviour on chlorite as revealed by scanning probe microscopy and density functional simulations

Pioneering electron energy loss spectroscopy (EELS) measurements of α-Bi2O3 are performed on three samples obtained through different synthesis methods. Experimental low-loss and core-loss EELS spectra are acquired. By combining them with detailed structural characterization and Density Functional Theory (DFT) simulations, we are able to detect and evaluate the presence of oxygen vacancies in the samples. This type of information has not been accessed previously from EELS data in bismuth oxide, because high-resolution EELS spectra or how vacancies reflect in Bi2O3 spectra were unreported. This novel measurement is further validated through comparison with photoluminescence data. Therefore, the technique has the ability to probe oxygen vacancies in Bi2O3 at an unprecedented resolution, which might allow solving material science and technological issues related to this material.