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Dewetting of monolayer water and isopropanol between MoS2 nanosheets
摘要： Understanding dewetting of solvent molecules confined to layered material (LM) interfaces is crucial to the synthesis of two-dimensional materials by liquid-phase exfoliation. Here, we examine dewetting behavior of water and isopropanol/water (IPA/H2O) mixtures between molybdenum disulfide (MoS2) membranes using molecular dynamics (MD) simulations. We find that a monolayer of water spontaneously ruptures into nanodroplets surrounded by dry regions. The average speed of receding dry patches is close to the speed of sound in air. In contrast, monolayer mixtures of IPA/H2O between MoS2 membranes slowly transform into percolating networks of nanoislands and nanochannels in which water molecules diffuse inside and IPA molecules stay at the periphery of islands and channels. These contrasting behaviors may explain why IPA/H2O mixtures are much more effective than H2O alone in weakening interlayer coupling and exfoliating MoS2 into atomically thin sheets.
关键词： molecular dynamics simulations,liquid-phase exfoliation,isopropanol/water mixtures,two-dimensional materials,layered material interfaces,dewetting,solvent molecules,MoS2 membranes
更新于2025-09-10 09:29:36
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Graphene oxide model with desirable structural and chemical properties
摘要： Due to unique chemical, electrical and optical properties, graphene oxide has been widely used as a promising candidate for many applications. Theoretical GO models developed so far present a good description of its chemical structure. However, when it comes to the structural properties, such as the size and distribution of vacancy defects, the curvature (or roughness), there exist significant gaps between computational models and experimentally synthesized GO materials. In this work, we carry out reactive molecular dynamics simulations and use experimental characteristics to fine tune theoretical GO models. Attentions have been paid to the vacancy defects, the distribution and hybridization of carbon atoms, and the overall C/O ratio of GO. The GO models proposed in this work have been significantly improved to represent quantitative structural details of GO materials synthesized via the modified Hummers method. The temperature-programmed protocol and the computational post analyses of Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, vacancy size and curvature distribution, are of general interest to a broad audience working on GO structures from other synthesis methods and other two-dimensional materials and their composites.
关键词： Chemical properties,Reactive molecular dynamics,Modified Hummers method,Graphene oxide,Structural properties
更新于2025-09-10 09:29:36
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Strength and toughness anisotropy in hexagonal boron nitride: An atomistic picture
摘要： Strength and toughness are two crucial mechanical properties of a solid that determine its ability to function reliably without undergoing failure in extreme conditions. While hexagonal boron nitride (hBN) is known to be elastically isotropic in the linear regime of mechanical deformation, its directional response to extreme mechanical loading remains less understood. Here, using a combination of density functional theory calculations and molecular dynamics simulations, we show that strength and crack nucleation toughness of pristine hBN are strongly anisotropic and chirality dependent. They vary nonlinearly with the chirality of the lattice under symmetry breaking deformation, and the anisotropic behavior is retained over a large temperature range with a decreasing trend at higher temperatures. An atomistic analysis reveals that bond deformation and associated distortion of electron density are nonuniform in the nonlinear regime of mechanical deformation, irrespective of the loading direction. This nonuniformity forms the physical basis for the observed anisotropy under static conditions, whereas reduction in nonuniformity and thermal softening reduce anisotropy at higher temperatures. The chirality-dependent anisotropic effects are well predicted by inverse cubic polynomials.
关键词： chirality,anisotropy,hexagonal boron nitride,molecular dynamics simulations,density functional theory,strength,toughness
更新于2025-09-10 09:29:36
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Coupling to Charge Transfer States Is the Key to Modulate the Optical Bands for Efficient Light-Harvesting in Purple Bacteria.
摘要： The photosynthetic apparatus of purple bacteria uses exciton delocalization and static disorder to modulate the position and broadening of its absorption bands, leading to efficient light harvesting. Its main antenna complex, LH2, contains two rings of identical bacteriochlorophyll pigments, B800 and B850, absorbing at 800 nm and at 850 nm, respectively. It has been an unsolved problem why static disorder of the strongly coupled B850 ring is several times larger than that of the B800 ring. Here we show that mixing between excitons and charge transfer states in the B850 ring is responsible for the effect. The linear absorption spectrum of the LH2 system is simulated by using a multi-scale approach with an exciton Hamiltonian generalized to include the charge transfer states that involve adjacent pigment pairs, with static disorder modelled microscopically by molecular dynamics simulations. Our results show that a sufficient inhomogeneous broadening of the B850 band, needed for efficient light-harvesting, is only obtained by utilizing static disorder in the coupling between local excited and inter-pigment charge transfer states.
关键词： exciton delocalization,B850,B800,charge transfer states,purple bacteria,LH2,molecular dynamics simulations,static disorder,bacteriochlorophyll pigments,photosynthetic apparatus,light harvesting
更新于2025-09-10 09:29:36
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tilt Grain Boundary on Oxygen-ion movement In Yttria-Stabilized Zirconia: Insights from molecular dynamics
摘要： We present a new methodology for investigating the combined effect of the Σ5(310)/[001] symmetric tilt grain boundary (GB) and the local cation environment in polycrystalline yttria stabilized zirconia (YSZ) on two important quantities that determine the ionic conductivity, namely, (i) the local hopping rate of O2- ion and (ii) the probability of O2--ion -vacancy pairs within the YSZ structure. How these quantities vary with distance to the GB core are estimated for the first time using waiting time distributions associated with O2- ion hop events in molecular dynamics simulations. We conclude that indeed fewer hop events occur in the presence of a GB. However, the GB effect can be felt at a far greater distance than previously believed. Most importantly, interactions between the O2- ions, nearby cations and the GB results in a hopping behavior that is different from one observed in single-crystal YSZ. Anisotropy in O2- ion movement in the vicinity of the GB is also studied. These results and the use of our novel technique have a direct implication on the development of improved models for ionic conduction in solid state electrolytes.
关键词： Ionic conductivity,molecular dynamics,yttria stabilized zirconia,grain boundary
更新于2025-09-10 09:29:36
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Tensile mechanical properties and fracture behavior of monolayer InSe under axial tension
摘要： Based on a newly developed interatomic potential, the mechanical properties and fracture behavior of monolayer InSe are investigated by using the classical molecular dynamics method. We ?nd that monolayer InSe exhibits excellent mechanical properties comparing with other two-dimensional materials. Especially, it can sustain an axial tensile strain of 27% in the zigzag direction at room temperature 300 K. Furthermore, the numerical results indicate that the monolayer InSe has an isotropy in the mechanical behaviors with the Youngs modulus being about 43 N/m both in the armchair and zigzag directions. We also discuss the e?ects of temperature and strain rate on the mechanical properties of monolayer InSe and ?nd the high temperature-sensitivity. It’s found that the mechanical properties signi?cantly decrease as the increasing temperature. In contrast, the mechanical properties has a relatively weak dependence on the strain rate. As the strain rate increases from 0.0002 to 0.0008 ps?1, Young’s modulus nearly keeps a constant. The fracture stress and strain in armchair direction only increase by 3.6% and 8.3%, respectively.
关键词： Tensile strain,Monolayer InSe,Molecular dynamics simulation,Two-dimensional materials,Mechanical property
更新于2025-09-10 09:29:36
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Structural evolution of oxygen on the surface of TiAlN: Ab initio molecular dynamics simulations
摘要： We have employed ab initio molecular dynamics simulations to study the oxidation behavior of TiAlN hard coatings as a function of Al content and temperature. Results show that for TiAlN with a low Al content (Ti0.75Al0.25N), Ti atoms can always bond with O atoms, while Al atoms bond with O only at a higher temperature. For Ti0.5Al0.5N, both Al and Ti can bond with O atoms, irrespective of temperature. Through analyzing the displacement height of O-bonded metal atoms, we suggest that titanium oxide nucleates at the outermost layer of Ti0.75Al0.25N while the outermost layer after Ti0.5Al0.5N is exposed to oxygen is aluminum oxide. Our simulation results predict, in agreement with experiment, that Ti0.5Al0.5N has superior oxidation resistance in comparison with Ti0.75Al0.25N. This study provides an atomistic insight to the initial stage of the oxidation process, which is else di?cult to observe experimentally.
关键词： Oxidation,TiAlN,Hard coating,Ab initio molecular dynamics
更新于2025-09-10 09:29:36
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Investigation on the phase transformation of monocrystalline silicon during nanoindentation at cryogenic temperature by molecular dynamics simulation
摘要： High-pressure phase transformation of silicon is an important phenomenon as it is of scientific and technological importance for semiconductor industry and micro/nano electromechanical system. However, there are limited studies on the phase transformation at cryogenic temperature. In this study, molecular dynamics simulation was conducted to investigate the nanoindentation of monocrystalline silicon at 1 K. The force-displacement curve and the corresponding phase transformation were studied in details. During the loading process, the contact zone was affected by the applied stress and the original diamond cubic structure of Si was distorted. With the increase of the depth, the distorted diamond cubic structure (DDS) was transformed into body-centered-tetragonal structure (bct-5) and Si-II. With the release of the force, the reverse transformations of Si-II to Si-III and Si-XII in junction with the pop-out events in the unloading curves can be clearly seen. It was also found that the phase distribution during the reverse transformation was strongly influenced by the indenter radius and indentation depth due to the different stress fields. At the higher depth, the unloading curves showed the unusual absence of pop-out and the appearance of surface extrusion. This can be ascribed by that the retained DDS outside the indentation after unloading not only restricts the transformation of Si-II but also brings the material extrusion on the surface due to the residual internal stress.
关键词： Pop-out,Nanoindentation,Silicon,Molecular dynamics,Extrusion
更新于2025-09-10 09:29:36
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Enhancement of photoluminescence efficiency in GeSe ultrathin slab by thermal treatment and annealing: experiment and first-principles molecular dynamics simulations
摘要： The effect of thermal treatment and annealing under different temperatures from 100 °C to 250 °C on the photoluminescence spectroscopy of the GeSe ultrathin slab is reported. After the thermal treatment and annealing under 200 °C, we found that the photoluminescence intensity of A exciton and B exciton in GeSe ultrathin slab is increased to twice as much as that in untreated case, while is increased by ~84% in the photoluminescence intensity of C exciton. Combined by our experimental work and theoretical simulations, our study confirms the significant role of thermal treatments and annealing in reducing surface roughness and removing the Se vacancy to form more compact and smoother regions in GeSe ultrathin slab. Our findings imply that the improved quality of GeSe surface after thermal treatments is an important factor for the photoluminescence enhancement.
关键词： annealing,ultrathin slab,first-principles molecular dynamics,GeSe,photoluminescence,thermal treatment
更新于2025-09-10 09:29:36
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Nano-scale wave dispersion beyond the First Brillouin Zone simulated with inertia gradient continua
摘要： Nano-scale wave dispersion beyond the First Brillouin Zone is often observed as descending branches and inflection points when plotting frequency or phase velocity against the wave number. Modeling this with discrete chain models is hampered by their restricted resolution. A continuum model equipped with higher-order inertia gradients is here developed as a suitable and versatile alternative. This model can be derived from discrete chain models, thereby providing a lower-scale motivation for the higher-order gradient terms. The derived gradient model is without free parameters, as the material constants are calculated a priori by minimising the error with respect to the discrete chain response. Unlike asymptotic approximations that provide a best fit for vanishing wave numbers, the error is here minimised over the entire range of reduced wave numbers 0 to 1, which leads to a much improved accuracy beyond the First Brillouin Zone. The new gradient model has been validated against (i) phonon dispersion curves measured through neutron scattering experiments in bismuth, aluminum, and nickel and (ii) Molecular Dynamics (MD) flexural wave propagation simulations of carbon nanotubes. The model captures all qualitative aspects of the experimental and MD dispersion curves without requiring a bespoke curve fitting procedure. With the exception of one set of MD results, the accuracy of the gradient model is very good.
关键词： Nano-scale wave dispersion,Molecular Dynamics,First Brillouin Zone,inertia gradient continua,carbon nanotubes,phonon dispersion curves
更新于2025-09-10 09:29:36