The Experts below are selected from a list of 41760 Experts worldwide ranked by ideXlab platform
Michele Parrinello - One of the best experts on this subject based on the ideXlab platform.
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naphthalene crystal shape prediction from molecular dynamics simulations
CrystEngComm, 2019Co-Authors: Zoran Bjelobrk, Michele Parrinello, Pablo M Piaggi, Thilo Weber, Tarak Karmakar, Marco MazzottiAbstract:We used molecular dynamics simulations to predict the steady state crystal shape of naphthalene grown from ethanol solution. The simulations were performed at constant supersaturation by utilizing a recently proposed algorithm [Perego et al., J. Chem. Phys., 2015, 142, 144113]. To bring the crystal growth within the timescale of a molecular dynamics simulation we applied well-tempered metadynamics with a spatially constrained collective variable, which focuses the sampling on the growing layer. We estimated that the resulting steady state crystal shape corresponds to a rhombic prism, which is in line with experiments. Further, we observed that at the investigated supersaturations, the {00} face grows in a two step two dimensional Nucleation Mechanism while the considerably faster growing faces {10} and {20} grow new layers with a one step two dimensional Nucleation Mechanism.
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Nucleation Mechanism for the direct graphite to diamond phase transition
Nature Materials, 2011Co-Authors: Rustam Z Khaliullin, Jörg Behler, Hagai Eshet, Thomas D Kuhne, Michele ParrinelloAbstract:Graphite remains stable at pressures higher than those of its equilibrium coexistence with diamond. This has proved hard to explain, owing to the difficulty in simulating the transition with accuracy. Ab initio calculations using a trained neural-network potential now show that the stability of graphite and the direct transformation of graphite to diamond can be accounted for by a Nucleation Mechanism.
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Nucleation Mechanism for the direct graphite to diamond phase transition
arXiv: Materials Science, 2011Co-Authors: Rustam Z Khaliullin, Jörg Behler, Hagai Eshet, Thomas D Kuhne, Michele ParrinelloAbstract:Graphite and diamond have comparable free energies, yet forming diamond from graphite is far from easy. In the absence of a catalyst, pressures that are significantly higher than the equilibrium coexistence pressures are required to induce the graphite-to-diamond transition. Furthermore, the formation of the metastable hexagonal polymorph of diamond instead of the more stable cubic diamond is favored at lower temperatures. The concerted Mechanism suggested in previous theoretical studies cannot explain these phenomena. Using an ab initio quality neural-network potential we performed a large-scale study of the graphite-to-diamond transition assuming that it occurs via Nucleation. The Nucleation Mechanism accounts for the observed phenomenology and reveals its microscopic origins. We demonstrated that the large lattice distortions that accompany the formation of the diamond nuclei inhibit the phase transition at low pressure and direct it towards the hexagonal diamond phase at higher pressure. The Nucleation Mechanism proposed in this work is an important step towards a better understanding of structural transformations in a wide range of complex systems such as amorphous carbon and carbon nanomaterials.
Minsheng Huang - One of the best experts on this subject based on the ideXlab platform.
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influences of particle size and interface energy on the stress concentration induced by the oblate spheroidal particle and the void Nucleation Mechanism
International Journal of Solids and Structures, 2006Co-Authors: Minsheng HuangAbstract:Abstract Separation of the particle–matrix interface and breakage of the second-phase particle are two main void Nucleation Mechanisms, which are directly associated with the stress concentration factors (SCFs) at the interface and within the particle, respectively. This work investigates the coupled effects of particle size and particle shape on these stress concentrations by solving an infinite solid containing an oblate spheroidal particle under remote stress boundary condition. The phenomenological strain plasticity theory by Fleck–Hutchinson [Fleck, N.A., Hutchinson, J.W., 1997. Strain gradient plasticity. In: Hutchinson, J.W., Wu, T.Y. (Eds.), Advance in Applied Mechanics, vol. 33. Academic Press, New York, pp. 295–361] is adopted to capture the size effect, various particle aspect ratios are considered to depict the particle shape effect and an interfacial energy concept is introduced to settle the double-traction equilibrium problem at the matrix–particle interface. By using a Ritz procedure, solutions about the stress concentrations are numerically achieved and three main results are found. First, the interfacial normal stress near the particle pole, the interfacial shear stress and the particle opening stress are dramatically elevated and their distributions are significantly modified by decrease in the particle size. Second, this particle size effect is influenced by the remote effective strain, remote stress triaxiality and the interfacial energy to different extent. Finally, the particle shape effect is coupled with this particle size effect, and the more oblate the particle is, the more significant the size effect on SCF elevation is. These findings are helpful for us to understand deeply the void Nucleation Mechanism at the micron scale.
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size effects on stress concentration induced by a prolate ellipsoidal particle and void Nucleation Mechanism
International Journal of Plasticity, 2005Co-Authors: Minsheng HuangAbstract:Abstract There generally exist two void Nucleation Mechanisms in materials, i.e. the breakage of hard second-phase particle and the separation of particle–matrix interface. The role of particle shape in governing the void Nucleation Mechanism has already been investigated carefully in the literatures. In this study, the coupled effects of particle size and shape on the void Nucleation Mechanisms, which have not yet been carefully addressed, have been paid to special attention. To this end, a wide range of particle aspect ratios (but limited to the prolate spheroidal particle) is considered to reflect the shape effect; and the size effect is captured by the Fleck–Hutchinson phenomenological strain plasticity constitutive theory (Advance in Applied Mechanics, vol. 33, Academic Press, New York, 1997, p. 295). Detailed theoretical analyses and computations on an infinite block containing an isolated elastic prolate spheroidal particle are carried out to light the features of stress concentrations and their distributions at the matrix–particle interface and within the particle. Some results different from the scale-independent case are obtained as: (1) the maximum stress concentration factor (SCF) at the particle–matrix interface is dramatically increased by the size effect especially for the slender particle. This is likely to trigger the void Nucleation at the matrix–particle interface by cleavage or atomic separation. (2) At a given overall effective strain, the particle size effect significantly elevates the stress level at the matrix–particle interface. This means that the size effect is likely to advance the interface separation at a smaller overall strain. (3) For scale-independent cases, the elongated particle fracture usually takes place before the interface debonding occurs. For scale-dependent cases, although the SCF within the particle is also accentuated by the particle size effect, the SCF at the interface rises at a much faster rate. It indicates that the probability of void Nucleation by the interface separation would increase.
Wei Huang - One of the best experts on this subject based on the ideXlab platform.
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the Nucleation Mechanism of succinic acid involved sulfuric acid dimethylamine in new particle formation
Atmospheric Environment, 2021Co-Authors: Zhongquan Wang, Yirong Liu, Chunyu Wang, Shuai Jiang, Yajuan Feng, Teng Huang, Wei HuangAbstract:Abstract Succinic acid (SUA) is a common dicarboxylic acid frequently observed in aerosols. Understanding the role of succinic acid in atmospheric new particle formation is essential to study the complicated Nucleation Mechanism. In this study, high-precision quantum chemical calculations and atmospheric clusters dynamic code (ACDC) simulations are used to investigate the Nucleation Mechanism of the (SA)x(SUA)y(DMA)z (0 = x, y, z ≤ 3) multicomponent system. The most stable molecular structures show that SUA can form relatively stable clusters with the SA-DMA system by hydrogen bond and proton-transfer interactions. Similar to SA molecules, SUA can provide protons to DMA when excess DMA molecules are available. ACDC simulations indicate that SUA can contribute to the cluster formation, especially at low sulfuric acid concentration and high succinic acid concentration. Moreover, the main cluster flux out of the SUA-containing system is along the non-diagonal (the number of acid molecules is greater than that of base molecules), which is different from the pure SA-DMA system. These clusters are stable enough to be present at a fairly high concentration, and could be a platform for growth into the larger sizes. This organic acid involved cluster formation may explain high Nucleation rate at low sulfuric acid concentration and high organic acid concentration.
Shigenobu Ogata - One of the best experts on this subject based on the ideXlab platform.
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Mechanism transition and strong temperature dependence of dislocation Nucleation from grain boundaries an accelerated molecular dynamics study
Physical Review B, 2016Co-Authors: Yunjiang Wang, Liang Wan, Shigenobu OgataAbstract:Accelerated molecular dynamics reveals a Mechanism transition and strong temperature dependence of dislocation Nucleation from grain boundaries (GBs) in Cu. At stress levels up to $\ensuremath{\sim}90%$ of the ideal dislocation-Nucleation stress, atomic shuffling at the $E$ structural unit in a GB acts as a precursor to dislocation Nucleation, and eventually a single dislocation is nucleated. At very high stress levels near the ideal dislocation-Nucleation stress, a multiple dislocation is collectively nucleated. In these processes, the activation free energy and activation volume depend strongly on temperature. The strain-rate dependence of the critical Nucleation stress is studied and the result shows that the Mechanism transition from the shuffling-assisted dislocation-Nucleation Mechanism to the collective dislocation-Nucleation Mechanism occurs during the strain rate increasing from ${10}^{\ensuremath{-}4}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{to}\phantom{\rule{0.16em}{0ex}}{10}^{10}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$.
Helmut Grubmuller - One of the best experts on this subject based on the ideXlab platform.
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sequential water and headgroup merger membrane poration paths and energetics from md simulations
Biophysical Journal, 2020Co-Authors: Greg Bubnis, Helmut GrubmullerAbstract:Abstract Membrane topology changes such as poration, stalk formation, and hemi-fusion rupture are essential to cellular function, but their molecular details, energetics, and kinetics are still not fully understood. Here we present a unified energetic and mechanistic picture of metastable pore defects in tensionless lipid membranes. We used an exhaustive committor analysis to test and select optimal reaction coordinates and also to determine the Nucleation Mechanism. These reaction coordinates were used to calculate free energy landscapes that capture the full process and end states. The identified barriers agree with the committor analysis. To enable sufficient sampling of the complete transition path for our molecular dynamics simulations, we developed a novel "gizmo" potential biasing scheme. The simulations suggest that the essential step in the Nucleation is the initial merger of lipid headgroups at the nascent pore center. To facilitate this event, an indentation pathway is energetically preferred to a hydrophobic defect. Continuous water columns that span the indentation were determined to be on-path transients that precede the Nucleation barrier. This study gives a quantitative description of the Nucleation Mechanism and energetics of small metastable pores and illustrates a systematic approach to uncover the Mechanisms of diverse cellular membrane remodeling processes.
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sequential water and headgroup merger membrane poration paths and energetics from md simulations
bioRxiv, 2020Co-Authors: Greg Bubnis, Helmut GrubmullerAbstract:Membrane topology changes such as poration, stalk formation, and hemi-fusion rupture are essential to cellular function, but their molecular details, energetics, and kinetics are still not fully understood. Here we present a unified energetic and mechanistic picture of metastable pore defects in tensionless lipid membranes. We used an exhaustive committor analysis to test and select optimal reaction coordinates and also to determine the Nucleation Mechanism. These reaction coordinates were used to calculate free energy landscapes that capture the full process and end states. The identified barriers agree with the committor analysis. To enable sufficient sampling of the complete transition path for our atomistic simulations, we developed a novel "gizmo" potential biasing scheme. The simulations suggest that the essential step in the Nucleation is the initial merger of lipid headgroups at the nascent pore center. To facilitate this event, an indentation pathway is energetically preferred to a hydrophobic defect. Continuous water columns that span the indentation were determined to be on-path transients that precede the Nucleation barrier. This study gives a quantitative description of the Nucleation Mechanism and energetics of small metastable pores and illustrates a systematic approach to uncover the Mechanisms of diverse cellular membrane remodeling processes.
