AIMD Simulations Research Articles

Mechanistic study on C(sp2)–F bond activation by a Ni0(silyl)-ate complex: an outer-sphere pathway via Ni0-mediated nucleophilic aromatic substitution

DFT calculations and AIMD simulations reveal C(sp2)–F bond activation by a Ni0(silyl)-ate complex, involving an outer-sphere pathway via Ni0-mediated SNAr.

Electronic structure modification of SnO2 to accelerate CO2 reduction towards formate.

A systematic theoretical study probing the catalytic potential of metal-doped SnO2(110) was conducted. The incorporation of metals such as Zr, Ti, W, V, Hf, and Ge is shown to drive electron transfer to Sn. The increased charge of Sn is injected into anti-bonding orbitals, finely tuning the catalytic activity and reducing the overpotential to -0.34 V. AIMD simulations show the stability of the modified structures. This work sheds light on the rational design of low-cost metal oxides with a high catalytic performance for CO2ER to formate.

Strong mechanical anisotropy and an anisotropic Dirac state in 2D C5N3.

Two-dimensional (2D) carbon nitride materials have emerged as a versatile platform for the design of high-performance nanoelectronics, but strong anisotropy in 2D carbon nitrides has rarely been reported. In this work, a 2D carbon nitride with strong anisotropy composed of tetra-, penta-, and hexa-rings (named as TPH-C5N3) is proposed. This TPH-C5N3 exhibits both dynamical and mechanical stability. Furthermore, it also showcases remarkable thermal stability, reaching up to 2300 K, as evidenced by AIMD simulations conducted in an NVT environment utilizing the Nosé-Hoover thermostat. Significantly, TPH-C5N3 demonstrates high anisotropic ratios in its mechanical properties, positioning it as the frontrunner in the current carbon nitride systems. In addition, a Dirac cone with an anisotropic ratio of 55.8% and Fermi velocity of 7.26 × 105 m s-1 is revealed in TPH-C5N3. The nontrivial topological properties of TPH-C5N3 are demonstrated by a non-zero Z2 invariant and topologically protected edge states. Our study offers theoretical insights into an anisotropic 2D carbon nitride material, laying the groundwork for its design and synthesis.

Unveiling the underlying corrosion/corrosion-resistance mechanism of a novel corrosion-resistant high entropy alloy by experimental means and AIMD simulations

In this work, we designed a new corrosion resistant high entropy alloy (CR-HEA) FeCoCrNiMo0.1Nb0.1. Its microstructure, corrosion behavior and passive film properties were studied by micro-characterization and electrochemical tests. The corrosion/corrosion-resistance mechanism was further revealed by first-principles calculations at atomic level. It is found that the designed HEA consists of (Mo, Nb)-lean FCC phase and (Mo, Nb)-rich Laves phase. Due to the formation of compact and protective passive film, our HEA exhibits a superior comprehensive corrosion resistance in the H2SO4 solution. AIMD and DFT calculations indicate that corrosive species are more likely to adsorb on the FCC phase, i.e., the FCC phase is preferentially attacked. Additionally, OH and O are easier to adsorb on Cr, Mo, and Nb atoms. Thus a more stable passive film is formed on the (Mo, Nb)-rich Laves phase, which provides better protection for Laves phase.

Theoretical exploration of the molecular stacking and charge transfer mechanism of PBQx:Y6 OSCs

The stacking morphology of the active layer molecules of organic solar cells is closely related to the PCE performance. However, experimental techniques are difficult to observe the molecular conformation and dynamic evolution at the atomic scale, which limits the understanding of the active layer charge transfer mechanism and the design of high-performance material molecules. DFT and AIMD methods can simulate the dynamic evolution of molecules at the atomic scale, and we obtained the local molecular stacking morphology of the active layers of PBQx:Y6 (x = 5,6,7) systems by AIMD simulations. The results reveal that PBQ6:Y6 exhibits the highest number of continuous π-π stacking molecules and the best ordering. The relatively high ΔES1CTx (> 0.1 eV) of PBQ7:Y6 results in increased open-circuit voltage loss. Interestingly, we found that the near-overlapping stacking of the D/A interface not only enables S1/CTX hybridization to reduce ΔES1CTx, but also enables energy level inversion of T1 and 3CT1 state to inhibit the non-geminate exciton recombination pathway. This work provides a systematic theoretical exploration of the molecular stacking and charge transfer mechanisms in PBQx:Y6 OSCs, which offer valuable theoretical insights for the development of high-performance photovoltaic devices.

Vanadium-decorated 2D polyaramid material for high-capacity hydrogen storage: Insights from DFT simulations

Herein, systematic computational investigations comprising density functional theory and ab initio molecular dynamics simulations (AIMD) have been conducted to assess the viability of vanadium decoration over the newly synthesized 2D polyaramid material (2DPA-I) as a potentially reversible hydrogen storage substrate for light fuel cell vehicles. The binding energies of V at different positions over 2DPA-I were compared, and the optimum site for V decoration was in the plane of 2DPA-I. The H2 binding ability of V-decorated 2DPA-I was improved over that of pristine 2DPA-I by 185.71 %. A single V atom decorated over 2DPA-I can effectively bind 7 H2 molecules, with a gravimetric H2 storage capacity of ~7.3 wt% and desorption temperature ~330 K at a favourable binding energy window (~−0.4 eV) to facilitate reversible H2 binding. V-decorated 2DPA-I remained stable at elevated temperatures as verified by AIMD simulations, and a substantial energy barrier of ~3 eV exists for the movement of the V atom across the 2DPA-I surface. The interaction of V with 2DPA-I and H2 with V-decorated 2DPA-I proceeds with a charge flow from the V atom towards H2 and 2DPA-I, respectively. The binding energy and charge transfer analysis of the interaction of H2 with V-decorated 2DPA-I indicates possible Kubas interactions. We predict that V-decorated 2DPA-I has immense potential for on-board H2 storage applications in light fuel cell vehicles.

Computational screening of oxygen and sulfur decorated MXene supported transitions metal single-atom catalysts for hydrogen evolution reaction

Herein, we systematically performed the comparative analysis of 24 transition metals single-atom catalysts (SACs) supported on MXene (Mo2CT2; T = O or S) surface for hydrogen evolution reaction (HER) and investigated their electronic structures, geometries, stabilities, selectivity, and catalytic activities by using first-principles calculations. The molecular dynamics and thermal stabilities of MXene (Mo2CO2 and Mo2CS2) monolayers were first investigated by using AIMD simulations and phonon dispersion spectra. Based on the Volmer-Heyrovsky pathway, TM/Mo2CO2 (TM = Ti, V, Cr, Co, Mo, Tc, Ru) and TM/Mo2CS2(TM = Cr, Mn, Fe, Zn, Tc, Ru, W, Pt) SACs exhibited good catalytic performance for HER and their ΔGH* values are close to the optimum value (ΔGH* → 0). The calculated ΔGH* values of Ti/Mo2CO2, Mo/Mo2CO2, Tc/Mo2CO2, Ru/Mo2CO2, Zn/Mo2CS2, W/Mo2CS2, Cr/Mo2CS2, and Pt/Mo2CS2 are equal or better than Pt (111) catalyst, making them active and selective catalysts for HER. Moreover, Mo/Mo2CO2 and Pt/Mo2CS2 catalysts exhibited outstanding catalytic performance towards HER much better than the Pt (111) catalyst. Therefore, the present investigation would provide a useful guideline for experimentalists to design MXene-based transition metals SACs for HER and other electrochemical applications.

Purely single-bonded spiral nitrogen chains stabilized by trivalent lanthanum ions.

Inspired by the single-bonded nitrogen chains stabilized by tetravalent cerium, pentavalent tantalum, and hexavalent tungsten atoms, we explored the possibility of single-bonded nitrogen polymorphs stabilized by trivalent lanthanum ions. To achieve this, we utilized the crystal structure search method on the phase diagram of binary La-N compounds. We identified three novel thermodynamically stable phases, the C2/c LaN3, P-1 LaN4, and P-1 LaN8. Among them, the C2/c phase with infinite helical poly-N6 chains becomes thermodynamically stable above 50GPa. Each nitrogen atom in the poly-N6 chain acquires one extra electron, and the spiral chain is purely single-bonded. The C2/c phase has an indirect band gap of ∼1.6eV at 60GPa. Notably, the band gap exhibits non-monotonic behavior, decreases first and then increases with increasing pressure. This abnormal behavior is attributed to the significant bonding of two La-N bonds at around 35GPa. Phonon spectrum calculations and AIMD simulations have confirmed that the C2/c phase can be quenched to ambient conditions with slight distortion, and it exhibits excellent detonation properties. Additionally, we also discovered armchair-like nitrogen chains in LaN4 and the armchair and zigzag-like mixed nitrogen chains in LaN8. These results provide valuable insights into the electronic and bonding properties of nitrides under high pressure and may have important implications for the design and development of novel functional materials.

Unveiling the nature of glucose hydrogenation over Raney Ni: DFT and AIMD simulations

Glucose hydrogenation to sorbitol is a vital industrial reaction for the utilization of biomass. Generally, hydrogenation is catalyzed by the inexpensive Raney Ni catalyst which has good catalytic but suffers from poor stability and side reaction，and the mechanisms of glucose hydrogenation on Raney Ni surfaces is also unclear. This study combines density functional theory calculations, ab initio molecular dynamics simulations (AIMD), and experiments to reveal the nature of glucose hydrogenation on the (111), (200), and (220) surfaces of Ni catalyst. The DFT calculation results show that the (111) and (200) surfaces of Raney Ni are favorable for hydrogenation with 111-η2, 200-η2–1, 200-η2–3 adsorption configurations and adsorption energy is closely related to the rate-determining step. Furthermore, in-situ IR analysis and AIMD calculation confirm the existence of 111-η2 structure in hydrogenation, while electronic analysis demonstrates that improving the alignment of the nickel surface's d orbitals with the -CO bond's π orbitals can enhance both the adsorption and catalytic hydrogenation activity. In addition, the (220) surface is found to be responsible for the dehydrogenation of cyclic-glucose, and decreasing the percentage of the (220) surface and increasing the reaction temperature appropriately may be effective in inhibiting the side reaction. This paper not only reveals the nature of Raney Ni catalyzed glucose hydrogenation but also lights the direction for the design of highly efficient nickel-based catalysts.

Explore the feasibility of Janus 2H-VSeTe monolayer as anode material for Li ion battery

Two-dimensional (2D) materials as potential energy storage systems have received extensive attention due to their high energy density and rate performance. Here, the electronic properties and feasibility of Janus 2H-VSeTe monolayer as LIBs anode material are systematically investigated using the first-principles calculations. No imaginary frequency in the phonon spectrum and the absence of obvious deformation simulated by AIMD simulations at 300 K prove the dynamic and thermal stability of Janus 2H-VSeTe monolayer, respectively. The pure Janus 2H-VSeTe monolayer exhibits a small direct band gap semiconductor character. The Li atom adsorption can result in the increase of electronic states near Ef and a transform of metallic behavior, ensuring good conductivity for the Janus 2H-VSeTe monolayer. On the other hand, the adsorbed Li atoms are fully ionized to ensure the charge and discharge process by the Bader analysis. Through the climbing-image nudged elastic band method, two possible migration paths are considered on the Se and Te surfaces, respectively. The lowest potential barriers are 0.159 eV and 0.188 eV, respectively, which proves that there is a high ion migration rate during charge and discharge process. The OCV and multi-layer Li atoms adsorption suggest that the corresponding specific capacity is 416 mA h g−1 for the Janus 2H-VSeTe monolayer, which reveals that Janus 2H-VSeTe monolayer is one of the feasible candidates for LIBs anode materials.

Surface-functionalization induced spintronic and photocatalytic features in group-III monochalcogenide monolayers: A first-principles study

In this paper, based on first principles calculations, we propose functionalization of group-III monochalcogenides with halogen atoms to form Janus MXY (M = Al, Ga, In; X = Se, Te; Y = Br, I) monolayers with enhanced physical properties. Using phonon dispersion, formation energy and AIMD simulations, nine MXY monolayers are found to be highly stable. The proposed MXY structures are shown to be direct/indirect semiconductors with bandgaps in the range of 1.13 and 3.34 eV. With regard to SOC effect, large Rashba spin splitting is observed at the Γ-point of conduction band in all Janus MXY monolayers with the largest coefficient of 1.021 eVÅ for GaTeBr. Moreover, we apply vertical electric field and biaxial strain as methods to tune the electronic and spintronic properties of MXY monolayers and improve their potential applications in the future devices. Investigating band edge positions, we find that six MXY monolayers fulfil the band alignment requirement for overall water splitting. Finally, Optical absorption, spatial charge separation and Gibbs free energy profile as other factors to assess the efficiency of MXY photocatalysts are studied. We believe that our research can pave a solid way to tune the physical properties of group-III monochalcogenides for a wider range of applications.

Competitive Hydration Versus Migration of Pre‐hydrated Electrons for CO2 Reduction in Aqueous Solution Revealed by Ab Initio Molecular Dynamics Simulation

AbstractPhotoinjected excess electrons (EEs) can fulfill the direct reduction of CO2 (CO2R) in an aqueous solution. However, the underlying mechanism is still poorly understood, especially the EE dynamics, which govern reaction mechanisms. Here, using a hybrid functional‐based ab initio molecular dynamic simulation strategy, it accurately characterizes the dynamics details of CO2R by aqueous EEs in solution and uncovers the nature of how EEs migrate for efficient CO2R. The AIMD simulations reveal that the injected EEs undergo hydration with diverse hydrated forms (various pre‐hydrated/e−pre/e22−pre and hydrated/e−aq/e22−aq) and multiple reaction channels due to competition of hydration versus migration. Interestingly, all pathways go through the same relay state [CO22−]aq and reach the same product (HCOO−). The core process before [CO22−]aq is competitive electron hydration and possible e−pre‐migration featuring either slowly flowing or fast jumping mode, while that after [CO22−]aq is proton transfer catalyzed by H‐bonding network as a proton source. The nature is how the concerted hydration dynamics of EEs and target CO2 govern the reaction proceeding through modulating their energy gap . This study provides dynamics insights into CO2R in aqueous solution by diverse e−pre/e−aq and the proposed strategy can also be utilized to explore the reduction mechanisms based on pre‐solvated electrons in other media.

Coexistence of Cationic and Anionic Phosphate Moieties in Solids: Unusual but Not Impossible.

Phosphoric acid is commonly known either as a neutral molecule or as an anion (phosphate). We theoretically confirm by ab initio molecular dynamics simulations (AIMD) that a cationic form H4PO4+ coexists with the anionic form H2PO4- in the same salt. This paradoxical situation is achieved by partial substitution of Cs+ by H4PO4+ in CsH2PO4. Thus, HnPO4 acts simultaneously as both the positive and the negative ion of the salt. We analyze the dynamical protonation pattern within the unusual hydrogen bond network that is established between the ions. Our AIMD simulations show that a conventional assignment of protonation states of the phosphate groups is not meaningful. Instead, a better description of the protonation situation is achieved by an efficiently fractional assignment of the strongly hydrogen-bonded protons to both its nearest and next-nearest oxygen neighbors.

Hydride Locations and Planar σ‐Aromaticity in Hydrido‐Coinage‐Metal Clusters

AbstractThe atomic‐scale analysis of hydrides within metal clusters remains challenging due to the difficulties in performing spatially resolved characterization experiments. One important issue is understanding how hydrogens bond to metal atoms and their positions. The classification of hydride as either a ligand or doped metal is a difficult problem due to its different impacts on electronic structures of coinage metal (Cu, Ag, and Au) clusters. Here, geometric characteristics, stability and electronic properties of MnH (M=Cu, Ag and Au; n=2–9) clusters are investigated in detail. We find that structure transitions of CunH and AgnH occur at n=5, while all AunH are more inclined to planar configurations, where H atoms prefer to be located on the bridge positions of M−M regardless of different sizes and configurations. Among them, the planar M5H clusters have the same structural framework and higher stability than their neighbors. The AIMD simulations demonstrate that these three clusters still show excellent thermal stability at 700 K. The molecular orbitals and AdNDP analyses reveal that the M5H clusters exhibit three six‐center two‐electron σ bonds throughout whole structural spaces and conform to σ aromaticity rule, which are also further confirmed by the ELF, LOL and NICSzz‐scan analyses.

Structural, optoelectronic and photocatalytic properties of MX (M=Ga, In; X=S, Se, Te) contact with novel janus GaInS3 monolayers

Using DFT calculations, we have fabricated the MX-GaInS3 (M = Ga, In; X = S, Se, Te) van dar Waals Heterostructures (vdWHs) and systematically calculated the structural, electronic, optical and photocatalytic properties. The calculated binding energies and AIMD simulations confirm the robust evidence for the stability of MX-GaInS3 vdWHs. Despite of the indirect bandgap nature of MX (M = Ga, In; X = S, Se, Te) monolayer, interestingally MX-GaInS3 vdWHs are direct bandgap semiconductors with type-II band alignments. Charge density difference, bader charges and the average electrostatic potential are calculated to investigate the transfer of charges amoung the layers at the interface of MX-GaInS3 vdWHs. Using dispersion along high symmetry path by fitting the band edges, we have also calculated the effective mass of carriers in MX-GaInS3 vdWHs. Smaller effective mass with higher mobility of carrier, suggest MX-GaInS3 vdWHs best candidate for optoelectronic devices. Absorption spectra in term of ε2(ω) of MX-GaInS3 (M = Ga, In; X = S, Se, Te) vdWHs are also calculated and investigated in detail. Both the conduction and valence band edges in GaS-GaInS3 vdWHs straddle the standard redox band edge potentials, hence have the ability to perform both reduction and oxidation, confirming the potentiality for full water splitting at pH = 0.

Strain engineering of the electrocatalytic activity of nitrogen-rich BeN4 Dirac monolayer for hydrogen evolution reaction

The strong bond energy and short bond length of N≡N triple bond make it a challenging target for synthesizing nitrogen-rich compounds. However, recent research has successfully fabricated atomic-thick BeN4 layers under high pressure (Bykov et al., 2021). Beryllonitrene, a new 2D material, consists of a Be atom and polymeric nitrogen chains and has anisotropic Dirac cones located near the Fermi level. This distinguishes it from graphene, which has isotropic Dirac cones, bulk PtTe2 and 2D borophene, which have Dirac cones located far from the Fermi energy. The anisotropic Dirac cones in beryllonitrene result in ultrahigh carrier mobility and the potential for direction-dependent quantum devices. In this study, we systematically investigated the hydrogen evolution reaction (HER) catalytic activity of nitrogen-rich, non-precious BeN4 monolayer using first-principles DFT calculations. Our results demonstrate that BeN4 monolayer is thermally stable, and Be vacancy is the most energetically favorable site for hydrogen adsorption. We also found the Gibbs free energy (ΔGH∗) of H∗ coverage can be tuned to an optimal value of |ΔGH∗|≤ 0.2 eV through strain engineering, significantly enhancing the HER electrocatalytic activity of BeN4 monolayer. Furthermore, we examined both the homolytic Tafel reaction and heterolytic Heyrovsky reaction for HER mechanism using reaction kinetics and AIMD simulations. These findings can contribute to the development of high-performance, non-precious, and nitrogen-rich 2D catalysts for HER in future research.

Theoretical Investigation of the Properties of Pd2Cu Intermetallics and CO2 Hydrogenation to Ethanol Catalyzed on Pd2Cu (110)

Intermetallics or ordered alloys are catalytically more advantageous than solid solution alloys. The B2 phase Pd2Cu intermetallics exhibit excellent catalytic properties for CO2 hydrogenation to ethanol and other reactions. However, the crystal structure of Pd2Cu is unknown. With a self-coded program based on symmetry and atomic ratio, we combed and identified the Pd2Cu structure. The calculated (110) interlayer distance agrees with the experimental result acceptably. Lattice dynamics and AIMD simulations demonstrate the identified structure is stable. The calculated bond strength indicates that among the five types of bonds, the shorter Pd–Cu bond (SPd–Cu) plays the most important role in stabilizing the structure. Crystal orbital Hamilton population (COHP) analyses reveal that the 5s(Pd)–4p(Cu) interaction dominates the Pd–Cu bonding and the 5s(Pd)–5s(Pd) or the 4p(Cu)–4p(Cu) interaction contributes the most in the homonuclear Pd–Pd and Cu–Cu bonds. Investigations on the reaction mechanism proposed for CO2 hydrogenation to CH3CH2OH show that CH2OH to CH2+OH is the key step determining the production of ethanol, followed by CO2+H to COOH and COOH to CO+OH.

Dynamics of Interlayer Na-Ions in Ga-Substituted Na2Zn2TeO6 (NZTO) Studied by Variable-Temperature Solid-State 23Na NMR Spectroscopy and DFT Modeling.

Local Na-coordination and dynamics of Na2-xZn2-xGaxTeO6; x = 0.00 (NZTO), 0.05, 0.10, 0.15, 0.20, were studied by variable-temperature, 23Na NMR methods and DFT AIMD simulations. Structure and dynamics were probed by NMR in the temperature ranges of 100-293 K in a magnetic field of 18.8 T and from 293 up to 500 K in a magnetic field of 11.7 T. Line shapes and T1 relaxation constants were analyzed. At 100 K, the otherwise dynamic Na-ions are frozen out on the NMR time scale, and a local structure characterization was performed for Na-ions at three interlayer sites. On increasing the temperature, complex peak shape coalescences occurred, and at 293 K, the Na NMR spectra showed some averaging due to Na-ion dynamics. A further increase to 500 K did not reveal any new peak shape variations until the highest temperatures, where an apparent peak splitting was observed, similar to what was observed in the 18.8 T experiments at lower temperatures. A three-site exchange model coupled with reduced quadrupolar couplings due to dynamics appear to explain these peak shape observations. The Ga substitution increases the Na-jumping rate, as proved by relaxation measurements and by a decrease in temperature for peak coalescence. The estimated activation energy for Na dynamics in the NZTO sample, from relaxation measurements, corresponds well to results from DFT AIMD simulations. Upon Ga substitution, measured activation energies are reduced, which is supported, in part, by DFT calculations. Addressing the correlated motion of Na-ions appears important for solid-state ion conductors since benefits can be gained from the decrease in activation energy upon Ga substitution, for example.

Theoretical investigation on CO oxidation by single nickel atom within two-dimensional porphyrin sheet

Catalysts for CO oxidation are usually precious metals, whose high cost restricts their widespread use. In order to reduce costs and improve catalytic activity, a two-dimensional porphyrin sheet with single nickel atoms (Ni−TDPS) was used as a catalyst for CO oxidation, and the detailed reaction path was studied by DFT. The stability of Ni−TDPS was determined by AIMD simulations. Three typical reaction mechanisms of CO oxidation on Ni−TDPS were discussed, including LH, ER, and TER mechanisms. The results showed that the TER mechanism is feasible due to the minimum reaction energy barrier in the rate-determining step. Therefore, Ni−TDPS is a potential candidate catalyst for CO oxidation in theory.

New Insights into Adsorption Properties of the Tubular Au26 from AIMD Simulations and Electronic Interactions

Recently, we revealed the electronic nature of the tubular Au26 based on spherical aromaticity. The peculiar structure of the Au26 could be an ideal catalyst model for studying the adsorptions of the Au nanotubes. However, through Google Scholar, we found that no one has reported connections between the structure and reactivity properties of Au26. Here, three kinds of molecules are selected to study the fundamental adsorption behaviors that occur on the surface of Au26. When one CO molecule is adsorbed on the Au26, the σ-hole adsorption structure is quickly identified as belonging to a ground state energy, and it still maintains integrity at a temperature of 500 K, where σ donations and π-back donations take place; however, two CO molecules make the structure of Au26 appear with distortions or collapse. When one H2 is adsorbed on the Au26, the H-H bond length is slightly elongated due to charge transfers to the anti-bonding σ* orbital of H2. The Au26-H2 can maintain integrity within 100 fs at 300 K and the H2 molecule starts moving away from the Au26 after 200 fs. Moreover, the Au26 can act as a Lewis base to stabilize the electron-deficient BH3 molecule, and frontier molecular orbitals overlap between the Au26 and BH3.