Ab Initio Molecular Calculations Research Articles

CO oxidation on single Pt atom supported by two-dimensional ZnO monolayer: Reaction mechanism and precursor activation

CO oxidation is an effective solution for controlling CO emissions, and supported single-atom catalysts have shown excellent catalytic reactivity for chemical reactions. CO oxidation on a single Pt atom supported by a two-dimensional ZnO monolayer is investigated by combing ab initio molecular dynamics and density functional theory calculations. Seven reaction mechanisms are identified, including two new trimolecular Elie-Riedel mechanisms; six of them, except for the Mars-van Krevelen mechanism, have rate-limiting step energy barriers between 0.31 and 0.47 eV, which is lower than the experimental activation barrier of 0.81 eV on single Pt atoms supported by bulk ZnO, and is much lower than that of about 1.0 eV on Pt(111) surface. Furthermore, two preferred reaction mechanisms are discovered, an Eley-Rideal mechanism and a trimolecular Eley-Rideal mechanism, both of which have rate-limiting step energy barriers as low as 0.31 eV. Our results show that the more antibonding orbitals are filled in the reaction precursor, the higher its activation level. Activation of precursors plays an important role in CO oxidation and leads to different mechanisms. These results provide insights into the design of efficient single-atom catalysts supported by two-dimensional materials for the removal of CO pollutants.

In-situ formed stable Pt nanoclusters on ceria-zirconia solid solutions induced by hydrothermal aging for efficient low-temperature CO oxidation

Pt nanoclusters (PtC) on the surface of ceria-zirconia solid solutions exhibit superior low-temperature CO oxidation activity compared to Pt single atoms (Pt1). However, the redispersion behavior of the PtC to Pt1 lowers the efficiency of CO Oxidation. In this work, the stable surface hydroxyl groups were constructed by high-temperature hydrothermal aging treatment. Specifically, the Pt1 catalyst (Pt/CZOe-SA) prepared by atom trapping was subjected to high-temperature hydrothermal treatment to obtain the stable PtC catalyst (Pt/CZOe-HT) with in-situ formed PtC. The experimental results showed that PtC with 2–3 nm size could achieve excellent low-temperature activity and thermal stability. In addition, the ab initio molecular dynamics and density functional theory calculations revealed the specific evolution process of dynamic dispersion for PtC with or without hydroxyl groups from the femtosecond scale, suggesting that the hydroxyl groups limited the dispersion of PtC in the form of “energy fence”. The hydrothermal treatment not only introduced high-temperature stable hydroxyl groups to improve the stability of the in-situ formed PtC, but also optimized the ratio of Pt1 and PtC, and then enhanced the low-temperature activity by the synergistic effect between Pt1 and PtC. The present work can provide theoretical guidance for developing high-performance and high-stability Pt-based catalysts.

Theoretical insights into the diverse stabilizing effects of fenchyl alcohol/thymol eutectic solvent on carotenoids

Carotenoids, a class of vital natural pigments, are known for their antioxidant properties and are integral to various industrial applications. However, their instability during processing and storage has limited their broader utilization. This study investigated the stabilizing effects of a fenchyl alcohol/thymol-based deep eutectic solvent (DES) on a spectrum of carotenoids, including lutein, zeaxanthin, astaxanthin, and β-carotene. Through a combination of ab initio molecular dynamics (AIMD) simulations and quantum chemical calculations, we elucidated the molecular interactions and stabilization mechanisms within the DES environment (methanol as the benchmark). Our findings reveal that the DES could exert varying degrees of influence on the stability of different types of carotenoids. The temperature-dependent behavior of carotenoids in the DES suggested a complex interplay between hydrogen bonding, dispersion forces, and the inherent structural properties of carotenoids. AIMD simulations provided a detailed picture of the structural organization and hydrogen bond network topology within the DES, highlighting the role of temperature on the stability and orientation of solvent molecules around carotenoids. Energy decomposition analysis (EDA), Hirshfeld surface analysis, and visual study of interactions further dissected the non-covalent interactions, emphasizing the significance of electrostatic and dispersion forces-driven non-covalent interactions (van der Waals dispersion interactions) in stabilizing carotenoids within the DES matrix. In comparison to methanol, the interactions between components of the eutectic system and the target molecules demonstrate enhanced dynamism, increased complementarity, and a greater variety of interaction patterns. This research presented a novel perspective on the use of DESs for the stabilization of carotenoids, offering potential solutions to enhance their industrial applicability and performance. The insights gained from this study are crucial for the development of sustainable and eco-friendly solvent systems, aligning with the growing demand for green chemistry in the pharmaceutical, cosmetic, and food industries.

Theoretical prediction of two-dimensional metallic AM2B8 (AM = K, Rb, Cs) as anode materials for Na-ion batteries

The development of two-dimensional anode materials with superior performance is becoming a critical undertaking for the advancement of Na-ion battery technology. Using isoelectronic substitution strategies, we predicted three alkali metal borides AM2B8 (AM = K, Rb, Cs) based on the SrB8 monolayer. Ab initio molecular dynamics simulations and phonon dispersion relationship calculations demonstrated their stability. Using density functional theory, we predict the feasibility of these three new metal nanosheets as anodes for Na-ion batteries. The AM2B8 monolayer retains its metallicity after the insertion of Na ions, ensuring that the anode has good electrical conductivity. In addition, AM2B8 has a low diffusion barrier and open circuit voltage (K2B8 is 0.08 eV and 0.26 V) during charge/discharge. In the voltage range that inhibits dendrite growth, K2B8 can reach the maximum theoretical specific capacity (326 mAh/g). These results indicate that AM2B8, especially K2B8, is a promising anode material for Na-ion batteries.

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.

Deep eutectic solvent-functionalized amorphous UiO-66 for efficient extraction and ultrasensitive analysis of perfluoroalkyl substances in infant milk powder

In this study, a convenient and effective method for determination of perfluoroalkyl substances (PFASs) in infant formula was developed based on a novel dispersive solid-phase extraction using deep eutectic solvent-functionalized amorphous UiO-66 (DES/aUiO-66) as sorbent. The synthesis of materials could be achieved without the use of complex and environmentally unfriendly procedures. Parameters were systematically investigated to establish a simple, fast, and efficient green pretreatment method. The method demonstrated high sensitivity, good precision, a detection limit of 0.330–0.529 ng·kg−1, and low matrix effects (< 12.8%). The mechanism for this material was elucidated by ab initio molecular dynamics (AIMD) simulations and quantum chemistry calculations. The presence of massive pore structures and collectively synergistic binding sites facilitated affinity adsorption toward PFASs. Finally, this method was applied to the monitoring of PFASs in 10 actual milk powder samples. This groundbreaking approach opens new possibilities for the advancement of analytical techniques and food safety monitoring.

Quantum Simulations and Experimental Insights into Glyphosate Adsorption Using Graphene-Based Nanomaterials.

The increasing global demand for food and agrarian development brings to light a dual issue concerning the use of substances that are crucial for increasing productivity yet can be harmful to human health and the environment when misused. Herein, we combine insights from high-level quantum simulations and experimental findings to elucidate the fundamental physicochemical mechanisms behind developing graphene-based nanomaterials for the adsorption of emerging contaminants, with a specific focus on pesticide glyphosate (GLY). We conducted a comprehensive theoretical and experimental investigation of graphene-based supports as promising candidates for detecting, sensing, capturing, and removing GLY applications. By combining ab initio molecular dynamics and density functional theory calculations, we explored several chemical environments encountered by GLY during its interaction with graphene-based substrates, including pristine and punctual defect regions. Our results unveiled distinct interaction behaviors: physisorption in pristine and doped graphene regions, chemisorption leading to molecular dissociation in vacancy-type defect regions, and complex transformations involving the capture of N and O atoms from impurity-adsorbed graphene, resulting in the formation of new GLY-derived compounds. The theoretical findings were substantiated by FTIR and Raman spectroscopy, which proposed a mechanism explaining GLY adsorption in graphene-based nanomaterials. The comprehensive evaluation of adsorption energies and associated properties provides valuable insights into the intricate nature of these interactions, shedding light on potential applications and guiding future experimental investigations of graphene-based nanofilters for water decontamination.

Surface-Enriched Room-Temperature Liquid Bismuth for Catalytic CO2 Reduction.

Bismuth-based electrocatalysts are effective for carbon dioxide (CO2) reduction to formate. However, at room temperature, these materials are only available in solid state, which inevitably suffers from surface deactivation, declining current densities, and Faradaic efficiencies. Here, the formation of a liquid bismuth catalyst on the liquid gallium surface at ambient conditions is shown as its exceptional performance in the electrochemical reduction of CO2 (i.e., CO2RR). By doping a trace amount of bismuth (740ppm atomic) in gallium liquid metal, a surface enrichment of bismuth by over 400 times (30 at%) in liquid state is obtained without atomic aggregation, achieving 98% Faradic efficiency for CO2 conversion to formate over 80 h. Ab initio molecular simulations and density functional theory calculations reveal that bismuth atoms in the liquid state are the most energetically favorable sites for the CO2RR intermediates, superior to solid Bi-sites, as well as joint GaBi-sites. This study opens an avenue for fabricating high-performing liquid-state metallic catalysts that cannot be reached by elementary metals under electrocatalytic conditions.

Unified deep learning network for enhanced accuracy in predicting thermal conductivity of bilayer graphene, hexagonal boron nitride, and their heterostructures

In this research, we utilized density functional theory (DFT) computations to perform ab initio molecular dynamics simulations and static calculations on graphene, hexagonal boron nitride, and their heterostructures, subjecting them to strains, perturbations, twist angles, and defects. The gathered energy, force, and virial information informed the creation of a training set comprising 1253 structures. Employing the Neural Evolutionary Potential framework integrated into Graphics Processing Units Molecular Dynamics, we fitted a machine learning potential (MLP) that closely mirrored the DFT potential energy surface. Rigorous validation of lattice constants and phonon dispersion relations confirmed the precision and dependability of the MLP, establishing a solid foundation for subsequent thermal transport investigations. A further analysis of the impact of twist angles uncovered a significant reduction in thermal conductivity, particularly notable in heterostructures with a decline exceeding 35%. The reduction in thermal conductivity primarily stems from the twist angle-induced softening of phonon modes and the accompanying increase in phonon scattering rates, which intensifies anharmonic interactions among phonons. Our study underscores the efficacy of the MLP in delineating the thermal transport attributes of two-dimensional materials and their heterostructures, while also elucidating the micro-mechanisms behind the influence of the twist angle on thermal conductivity, offering fresh perspectives for the design of advanced thermal management materials.

Transport coefficients of warm dense matter from Kohn-Sham density functional theory

We present a comprehensive study of transport coefficients including DC electrical conductivity and related optical properties, electrical contribution to the thermal conductivity, and the shear viscosity via ab initio molecular dynamics and density functional theory calculations on the “priority 1” cases from the “Second Charged-Particle Transport Coefficient Workshop” [Stanek et al., Phys. Plasmas (to be published 2024)]. The purpose of this work is to carefully document the entire workflow used to generate our reported transport coefficients, up to and including our definitions of finite size and statistical convergence, extrapolation techniques, and choice of thermodynamic ensembles. In pursuit of accurate optical properties, we also present a novel, simple, and highly accurate algorithm for evaluating the Kramers–Kronig relations. These heuristics are often not discussed in the literature, and it is hoped that this work will facilitate the reproducibility of our data.

Stability and Reactivity of Aromatic Radical Anions in Solution with Relevance to Birch Reduction.

We investigate the electronic structure of aromatic radical anions in the solution phase employing a combination of liquid-jet (LJ) photoelectron (PE) spectroscopy measurements and electronic structure calculations. By using recently developed protocols, we accurately determine the vertical ionization energies of valence electrons of both the solvent and the solute molecules. In particular, we first characterize the pure solvent of tetrahydrofuran (THF) by LJ-PE measurements in conjunction with ab initio molecular dynamics simulations and G0W0 calculations. Next, we determine the electronic structure of neutral naphthalene (Np) and benzophenone (Bp) as well as their radical anion counterparts Np- and Bp- in THF. Wherever feasible, we performed orbital assignments of the measured PE features of the aromatic radical anions, with comparisons to UV-vis absorption spectra of the corresponding neutral molecules being instrumental in rationalizing the assignments. Analysis of the electronic structure differences between the neutral species and their anionic counterparts provides understanding of the primarily electrostatic stabilization of the radical anions in solution. Finally, we obtain a very good agreement of the reduction potentials extracted from the present LJ-PES measurements of Np- and Bp- in THF with previous electrochemical data from cyclic voltammetry measurements. In this context, we discuss how the choice of solvent holds significant implications for optimizing conditions for the Birch reduction process, wherein aromatic radical anions play crucial roles as reactive intermediates.

Investigation of the effects of solvent on oxygen evolution reactions on the surface of magnesium oxide

In this research, due to the importance of oxygen evolution reactions (OER) in the production of hydrogen gas, the effects of the solvent on the OER steps on the magnesium oxide surface have been studied. For this purpose, the difference in free energy value in OER steps on the Magnesium oxide surface for two systems (in the presence and the absence of solvent) have been investigated using molecular dynamics (MD) simulation and thermodynamic integration (TI). These results are in perfect agreement with the results obtained from ab initio molecular dynamics simulations and quantum mechanics calculations. Our findings show that the presence of water solvent around the surface of magnesium oxide has a crucial role on OER and leads to an increase more than twofold in the free energy of all steps. Also, the presence of the solvent has the most effect on the third step of OER, and its ΔG increases by about 1.9 eV. This fact can be attributed to the approach of the water molecules to the substrate spontaneously, which increases the probability of forming hydrogen bonds and the number of contacts, leading to more favorable thermodynamic reactions. Close inspection of the calculated binding energies between the substrate and the intermediates confirms that the binding energy of OER's second step is significantly higher than the other steps and is the velocity determining step.

The coexistence of high piezoelectricity and superior optical absorption in Janus Bi2X2Y (X = Te, Se; Y = Te, Se, S) monolayers.

Bismuth chalcogenide and its derivatives have been attracting attention in various fields as semiconductors or topological insulators. Inspired by the high piezoelectric properties of Janus Bi2TeSeS monolayer and the excellent optical absorption properties of the Bi2X3 (X = Te, Se, S) monolayers, we theoretically predicted four new-type two-dimensional (2D) monolayers Janus Bi2X2Y (X = Te, Se; Y = Te, Se, S) using the first principles combined with density functional theory (DFT). The thermal, dynamic, and mechanical stabilities of Janus Bi2X2Y monolayers were confirmed based on ab initio molecular dynamics (AIMD) simulations, phonon dispersion, and elastic constants calculations. Their elastic properties, band structures, piezoelectric, and optical properties were systematically investigated. It was found that Janus Bi2X2Y monolayers have a typical Mexican hat-shaped valence band edge structure and, therefore, have a ring-shaped flat band edge, which results in their indirect band gaps. The results show that Janus Bi2X2Y monolayers are semiconductors with moderate band gaps (0.62-0.98 eV at the HSE + SOC level). After considering the electron-phonon renormalization (EPR), the band gaps are reduced by less than 5% at 0 K under the zero-point renormalization (ZPR) and further reduced by approximately 10% at 300 K. Besides, Janus Bi2X2Y monolayers also exhibit excellent optical absorption properties in the blue-UV light region, with the peak values at the order of 8 × 105 cm-1. Particularly, the Janus Bi2Te2S monolayer was found to exhibit a piezoelectric strain coefficient d11 of up to 20.30 pm V-1, which is higher than that of most of the 2D materials. Our results indicate that Janus Bi2X2Y monolayers could be promising candidates in solar cells, optical absorption, and optoelectronic devices; especially, a Janus Bi2Te2S monolayer can also be an excellent piezoelectric material with great prospects in the fields of mechanical and electrical energy conversion.

Can the presence of a fluorine-containing functional group in eutectic mixtures indeed bring fluorous affinity for fluorotelomer alcohol?

We focus on deep eutectic solvents (DESs) and investigate their potential for perfluoroalkyl substance (PFAS) remediation through ab initio molecular dynamics (AIMD) simulations and quantum chemistry calculations.

The potential of zero charge and solvation effects on single-atom M–N–C catalysts for oxygen electrocatalysis

Ab initio molecular dynamics and DFT calculations are comprehensively performed to investigate the linear correlation between the point of zero charge, solvation effects, and the binding energy of HO* adsorption on single-atom catalyst surface.

Temperature Dependence of the CdS Bandgap in the Extreme Confinement Regime.

A non-empirical equation describing the effect of size on the temperature dependence of the optical bandgap of CdS (dEg/dT) is obtained on the basis of the Brus equation. Intriguingly, we find that dEg/dT diverges strongly from bulk values only within the "extreme confinement" (EC) regime. We conducted both experimental and theoretical investigations of the absorption spectra of CdS clusters and quantum dots as a function of temperature above room temperature. Our results show that the value of dEg/dT obtained from absorption spectra in the EC regime is 2.5 times higher than in the strong confinement regime. Notable ligand sensitivities are also observed for dEg/dT in the case of CdS clusters. Ab initio molecular dynamics simulations and density functional theory calculations reveal that thermal fluctuations are the crucial factor influencing the bandgap temperature coefficient. Our results help resolve some long-standing debates regarding the dEg/dT behavior of semiconductor quantum dots.

Interface mediated CO2 hydrogenation on inverse supported ZrO2/Ni(1 1 1) nanocluster catalyst

To tune the activity and selectivity of CO2 hydrogenation, inverse supported Zr9O18/Ni(111) catalysts are designed based on ab initio molecular dynamics simulation and density functional theory calculation under the consideration of the number of interfacial O and Zr atoms as well as the interaction between O and Zr atoms. For the most stable catalyst with coordinatively unsaturated interface Zr sites, charge transfer from surface to oxide has been found. The Ni(111) surface is pre-covered by H atoms and the interface Zr sites can activate CO2 to a large extent, and their interaction results in the spontaneous formation of surface formate. Further hydrogenation of surface formate leads to the selective formation of methanol with an apparent Gibbs free energy barrier of 0.62 eV, lower than that of methane formation (1.09 eV). On the contrary to metallic nickel and supported nickel catalysts, the most favoured methanol formation route [HCOO → CHO → CH2O → CH3O → CH3OH] does not involve CO as intermediate, revealing the mediated interface effect.

Three‐Dimensional Porous Diboron Dinitride as a High‐Performance Anode Material for Sodium/Potassium‐Ion Batteries: A First Principles Study

Abstract2D boron nitride shows great promise in the photoelectric device, deep UV emitter and field effect transistor with good thermal stability, high mechanical robustness and chemical inertness; nonetheless, its inherently low electrical conductivity and small pore size have severely hindered the electrochemical kinetics and lead to a poor rate capability. Herein, we design a novel porous 3D−B2N2 structure by assembling the orthorhombic B2N2 monolayer into t‐C24 lattice and assesse its feasibility as the anode material of sodium(SIBs)/potassium(PIBs) ion batteries. The ab initio molecular dynamics (AIMD) simulation, Born‐Huang criteria, phonon spectrum and cohesive energy calculations confirms that the resulting 3D−B2N2 possesses excellent mechanical, thermal and dynamical stability. Different from the pristine h‐B2N2, an improved electrical conductivity is observed for 3D−B2N2 with a small band gap of 0.66 eV. Moreover, the low mass density, unique porous structure and strong adsorption energy make the 3D−B2N2 an outstanding electrode material for SIBs/PIBs with high storage capacities of 599.90 (479.92) mA h/g, low averaged open circuit voltages of 0.13 (0.27) V, low diffusion barriers of 0.04 (0.008) eV, and small volume expansions of 0.96 % (2.63 %). All the encouraging findings reveal that the 3D−B2N2 anode deserves further experimental investigation for SIBs/PIBs.

Hydrogen Bonds in Lead Halide Perovskites: Insights from Ab Initio Molecular Dynamics.

Hydrogen bonds (HBs) play an important role in the rotational dynamics of organic cations in hybrid organic/inorganic halide perovskites, thus affecting the structural and electronic properties of the perovskites. However, the properties and even the existence of HBs in these perovskites are not well established. In this study, we investigate HBs in perovskites MAPbBr3 (MA+ = CH3NH3+), FAPbI3 (FA+ = CH(NH2)2+), and their solid solution with composition (FAPbI3)7/8(MAPbBr3)1/8, using ab initio molecular dynamics and electronic structure calculations. We consider HBs donated by X-H fragments (X = N and C) of the organic cations and accepted by the halides (Y = Br and I) and characterize their properties based on pair distribution functions and on a combined distribution function of the hydrogen-acceptor distance with the donor-hydrogen-acceptor angle. By analyzing these functions, we establish geometrical criteria for HB existence based on the hydrogen-acceptor (H-Y) distance and donor-hydrogen-acceptor angle (X-H-Y). The distance condition is defined as d(H - Y) < 3 Å for N-H-donated HBs and d(H - Y) < 4 Å for C-H-donated HBs. The angular condition is 135° < (X - H - Y) < 180° for both types of HBs. A HB is considered to be formed when both angular and distance conditions are simultaneously satisfied. At the simulated temperature (350 K), the HBs dynamically break and form. We compute the time correlation functions of HB existence and HB lifetimes, which range between 0.1 and 0.3 ps at that temperature. The analysis of HB lifetimes indicates that N-H-Br bonds are relatively stronger than N-H-I bonds, while C-H-Y bonds are weaker, with a minimal influence from the halide and cation. To evaluate the impact of HBs on the vibrational spectra, we present the power spectrum in the region of N-H and C-H stretching modes, comparing them with the normal mode frequencies of isolated cations. We show that the peaks associated with N-H stretching modes in perovskites are redshifted and asymmetrically deformed, while the C-H peaks do not exhibit these effects.

Dynamic and static insights on the interaction mechanism between heavy metal contaminants in MSW incineration flue gas and modified carbon materials: Aggregation of PbO and CdO

Clarifying the interaction mechanism between heavy metals and adsorbent is the foundation to trigger the efficiency upgrades of adsorption technology. However, the existing studies ignore the coupling effect between heavy metal pollutants, which leads to a mismatch between theory and practice. Ab-initio molecular dynamics and density functional theory calculations are combined to uncover the dynamical interactions of mixed Pb/Cd species over the transition metal-modified carbon materials (CMs), discovering a new mechanism for enhanced heavy metal removal. Among various mixtures, PbO/CdO generates a stable and compact quadrilateral structure, greatly favorable for the nucleation and agglomeration of gas-phase heavy metals. According to the bond length tracking and electronic analyses, PbO plays an aggregating role and CdO plays a stabilizing role, resulting in dynamic stabilization of the tetragonal aggregates. Due to the different charge transfer and hybridization strengths between the surface-active sites and aggregates, the aggregates can only be stably trapped by Fe-modified CM. In addition, the Fe-modified CM exhibits excellent aggregation properties in the wide temperature region and in the low molecular environment. Overall, Fe-modified CM achieves synergistic removal of PbO and CdO, accommodating the environment of wide temperatures and low heavy metal concentrations, which provides an inspiration for the adsorbent design.