Wei Cai
Associate Professor of Mechanical Engineering and, by courtesy, of Materials Science and Engineering
Bio
Predicting mechanical strength of materials through theory and simulations of defect microstructures across atomic, mesoscopic and continuum scales. Developing new atomistic simulation methods for long time-scale processes, such as crystal growth and self-assembly. Introducing magnetic field in quantum simulations of electronic structure and transport.
Academic Appointments
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Associate Professor, Mechanical Engineering
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Associate Professor (By courtesy), Materials Science and Engineering
Honors & Awards
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Career Award, National Science Foundation (2006)
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Presidential Early Career Award, National Science and Technology Council (2004)
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Young Investigator Award, AFOSR (2006)
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Beer and Johnston Outstanding New Mechanics Educator Award, American Society for Engineering Education (2008)
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T. J. R. Hughes Young Investigator Award, ASME (2013)
Professional Education
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PhD, MIT, Nuclear Engineering (2001)
2015-16 Courses
- Imperfections in Crystalline Solids
ME 209 (Sum) - Introduction to Statistical Mechanics
ME 346A (Spr) - Mechanics - Elasticity and Inelasticity
ME 333B (Win) - Mechanics of Materials
ME 80 (Aut) - Seminar in Solid Mechanics
ME 395 (Spr) -
Independent Studies (8)
- Engineering Problems
ME 391 (Aut, Win, Spr, Sum) - Engineering Problems and Experimental Investigation
ME 191 (Aut, Win, Spr, Sum) - Experimental Investigation of Engineering Problems
ME 392 (Aut, Win, Spr, Sum) - Honors Research
ME 191H (Aut, Win, Spr, Sum) - Ph.D. Research
MATSCI 300 (Aut, Win, Spr, Sum) - Ph.D. Teaching Experience
ME 491 (Aut, Win, Spr, Sum) - Practical Training
ME 299A (Aut, Win, Spr, Sum) - Practical Training
ME 299B (Aut, Win, Spr, Sum)
- Engineering Problems
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Prior Year Courses
2014-15 Courses
- Imperfections in Crystalline Solids
ME 209 (Sum) - Mechanics - Elasticity and Inelasticity
ME 333B (Win) - Mechanics of Materials
ME 80 (Spr) - Seminar in Solid Mechanics
ME 395 (Aut)
2013-14 Courses
- Introduction to Molecular Simulations
ME 346B (Spr) - Introduction to Statistical Mechanics
ME 346A (Win) - Mechanics of Materials
ME 80 (Aut) - Seminar in Solid Mechanics
ME 395 (Win)
2012-13 Courses
- Imperfections in Crystalline Solids
ME 209 (Sum) - Theory and Application of Inelasticity
ME 342 (Spr) - Theory and Applications of Elasticity
ME 340 (Win)
- Imperfections in Crystalline Solids
All Publications
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Stochastic behaviors in plastic deformation of face-centered cubic micropillars governed by surface nucleation and truncated source operation
ACTA MATERIALIA
2015; 95: 176-183
View details for DOI 10.1016/j.actamat.2015.05.032
View details for Web of Science ID 000358626200019
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A Bamboo-Inspired Nanostructure Design for Flexible, Foldable, and Twistable Energy Storage Devices
NANO LETTERS
2015; 15 (6): 3899-3906
Abstract
Flexible energy storage devices are critical components for emerging flexible electronics. Electrode design is key in the development of all-solid-state supercapacitors with superior electrochemical performances and mechanical durability. Herein, we propose a bamboo-like graphitic carbon nanofiber with a well-balanced macro-, meso-, and microporosity, enabling excellent mechanical flexibility, foldability, and electrochemical performances. Our design is inspired by the structure of bamboos, where a periodic distribution of interior holes along the length and graded pore structure at the cross section not only enhance their stability under different mechanical deformation conditions but also provide a high surface area accessible to the electrolyte and low ion-transport resistance. The prepared nanofiber network electrode recovers its initial state easily after 3-folded manipulation. The mechanically robust membrane is explored as a free-standing electrode for a flexible all-solid-state supercapacitor. Without the need for extra support, the volumetric energy and power densities based on the whole device are greatly improved compared to the state-of-the-art devices. Even under continuous dynamic operations of forceful bending (90°) and twisting (180°), the as-designed device still exhibits stable electrochemical performances with 100% capacitance retention. Such a unique supercapacitor holds great promise for high-performance flexible electronics.
View details for DOI 10.1021/acs.nanolett.5b00738
View details for Web of Science ID 000356316900037
View details for PubMedID 26011653
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Intrinsic bauschinger effect and recoverable plasticity in pentatwinned silver nanowires tested in tension.
Nano letters
2015; 15 (1): 139-146
Abstract
Silver nanowires are promising components of flexible electronics such as interconnects and touch displays. Despite the expected cyclic loading in these applications, characterization of the cyclic mechanical behavior of chemically synthesized high-quality nanowires has not been reported. Here, we combine in situ TEM tensile tests and atomistic simulations to characterize the cyclic stress-strain behavior and plasticity mechanisms of pentatwinned silver nanowires with diameters thinner than 120 nm. The experimental measurements were enabled by a novel system allowing displacement-controlled tensile testing of nanowires, which also affords higher resolution for capturing stress-strain curves. We observe the Bauschinger effect, that is, asymmetric plastic flow, and partial recovery of the plastic deformation upon unloading. TEM observations and atomistic simulations reveal that these processes occur due to the pentatwinned structure and emerge from reversible dislocation activity. While the incipient plastic mechanism through the nucleation of stacking fault decahedrons (SFDs) is fully reversible, plasticity becomes only partially reversible as intersecting SFDs lead to dislocation reactions and entanglements. The observed plastic recovery is expected to have implications to the fatigue life and the application of silver nanowires to flexible electronics.
View details for DOI 10.1021/nl503237t
View details for PubMedID 25279701
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A three-dimensional phase field model for nanowire growth by the vapor-liquid-solid mechanism
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2014; 22 (5)
View details for DOI 10.1088/0965-0393/22/5/055005
View details for Web of Science ID 000338441700006
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Modeling a distribution of point defects as misfitting inclusions in stressed solids
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS
2014; 66: 154-171
View details for DOI 10.1016/j.jmps.2014.01.015
View details for Web of Science ID 000335635400010
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Ideal Shear Strength of a Quantum Crystal
PHYSICAL REVIEW LETTERS
2014; 112 (15)
Abstract
Using path-integral Monte Carlo simulations, we compute the ideal shear strength (ISS) on the basal plane of hcp (4)He. The failure mode upon reaching the ISS limit is characterized by the homogeneous nucleation of a stacking fault and it is found to be anisotropic, consistent with Schmid's law of resolved shear stress. Comparing the ISS of hcp (4)He to a large set of classical crystals shows that it closely fits the approximately universal modified Frenkel model of ideal strength. In addition to giving quantitative stress levels for the homogeneous nucleation of extended defects in hcp (4)He, our findings lend support to assumptions in the literature that inherently classical models remain useful for the description of mechanical behavior in quantum crystals.
View details for DOI 10.1103/PhysRevLett.112.155303
View details for Web of Science ID 000334597300007
View details for PubMedID 24785047
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Efficient time integration in dislocation dynamics
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2014; 22 (2)
View details for DOI 10.1088/0965-0393/22/2/025003
View details for Web of Science ID 000332834600003
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Stress dependence of cross slip energy barrier for face-centered cubic nickel
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS
2014; 62: 181-193
View details for DOI 10.1016/j.jmps.2013.09.023
View details for Web of Science ID 000329266600012
- Stress Dependence of Cross Slip Energy Barrier for Face-Centered Cubic Metals Journal of the Mechanics and Physics of Solids 2014; 62: 181
- Efficient Time Integrators for Dislocation Dynamics Simulations Modelling and Simulation in Materials Science and Engineering 2014; 24: 025003
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Zipping, entanglement, and the elastic modulus of aligned single-walled carbon nanotube films
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2013; 110 (51): 20426-20430
Abstract
Reliably routing heat to and from conversion materials is a daunting challenge for a variety of innovative energy technologies--from thermal solar to automotive waste heat recovery systems--whose efficiencies degrade due to massive thermomechanical stresses at interfaces. This problem may soon be addressed by adhesives based on vertically aligned carbon nanotubes, which promise the revolutionary combination of high through-plane thermal conductivity and vanishing in-plane mechanical stiffness. Here, we report the data for the in-plane modulus of aligned single-walled carbon nanotube films using a microfabricated resonator method. Molecular simulations and electron microscopy identify the nanoscale mechanisms responsible for this property. The zipping and unzipping of adjacent nanotubes and the degree of alignment and entanglement are shown to govern the spatially varying local modulus, thereby providing the route to engineered materials with outstanding combinations of mechanical and thermal properties.
View details for DOI 10.1073/pnas.1312253110
View details for Web of Science ID 000328548600031
View details for PubMedID 24309375
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Conditional convergence in two-dimensional dislocation dynamics
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2013; 21 (5)
View details for DOI 10.1088/0965-0393/21/5/055003
View details for Web of Science ID 000321288800003
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Atomistic simulations of grain boundary segregation in nanocrystalline yttria-stabilized zirconia and gadolinia-doped ceria solid oxide electrolytes
ACTA MATERIALIA
2013; 61 (10): 3872-3887
View details for DOI 10.1016/j.actamat.2013.03.027
View details for Web of Science ID 000319304400032
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Plasticity of bcc micropillars controlled by competition between dislocation multiplication and depletion
ACTA MATERIALIA
2013; 61 (9): 3233-3241
View details for DOI 10.1016/j.actamat.2013.02.011
View details for Web of Science ID 000318533500009
- Zipping, Entanglement, and the Modulus of Aligned Single-Walled Carbon Nanotube Films 2013
- Modelling plasticity of BCC micro-pillars using dislocation dynamics Acta Materialia 2013; 61: 3233
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Modeling Dislocation Mechanisms of the Acoustic Nonlinearity in Metallic Crystals
STRUCTURAL HEALTH MONITORING 2013, VOLS 1 AND 2
2013: 1065-1072
View details for Web of Science ID 000329292700130
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On the existence of Eshelby's equivalent ellipsoidal inclusion solution
MATHEMATICS AND MECHANICS OF SOLIDS
2012; 17 (8): 840-847
View details for DOI 10.1177/1081286511433082
View details for Web of Science ID 000310878600004
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Nucleation-Controlled Distributed Plasticity in Penta-twinned Silver Nanowires
SMALL
2012; 8 (19): 2986-2993
Abstract
A unique size-dependent strain hardening mechanism, that achieves both high strength and ductility, is demonstrated for penta-twinned Ag nanowires (NWs) through a combined experimental-computational approach. Thin Ag NWs are found to deform via the surface nucleation of stacking fault decahedrons (SFDs) in multiple plastic zones distributed along the NW. Twin boundaries lead to the formation of SFD chains that locally harden the NW and promote subsequent nucleation of SFDs at other locations. Due to surface undulations, chain reactions of SFD arrays are activated at stress concentrations and terminated as local stress decreases, revealing insensitivity to defects imparted by the twin structures. Thick NWs exhibit lower flow stress and number of distributed plastic zones due to the onset of necking accompanied by more complex dislocation structures.
View details for DOI 10.1002/smll.201200522
View details for Web of Science ID 000309454800010
View details for PubMedID 22829327
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Singular orientations and faceted motion of dislocations in body-centered cubic crystals
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2012; 109 (38): 15174-15178
Abstract
Dislocation mobility is a fundamental material property that controls strength and ductility of crystals. An important measure of dislocation mobility is its Peierls stress, i.e., the minimal stress required to move a dislocation at zero temperature. Here we report that, in the body-centered cubic metal tantalum, the Peierls stress as a function of dislocation orientation exhibits fine structure with several singular orientations of high Peierls stress-stress spikes-surrounded by vicinal plateau regions. While the classical Peierls-Nabarro model captures the high Peierls stress of singular orientations, an extension that allows dislocations to bend is necessary to account for the plateau regions. Our results clarify the notion of dislocation kinks as meaningful only for orientations within the plateau regions vicinal to the Peierls stress spikes. These observations lead us to propose a Read-Shockley type classification of dislocation orientations into three distinct classes-special, vicinal, and general-with respect to their Peierls stress and motion mechanisms. We predict that dislocation loops expanding under stress at sufficiently low temperatures, should develop well defined facets corresponding to two special orientations of highest Peierls stress, the screw and the M111 orientations, both moving by kink mechanism. We propose that both the screw and the M111 dislocations are jointly responsible for the yield behavior of BCC metals at low temperatures.
View details for DOI 10.1073/pnas.1206079109
View details for Web of Science ID 000309211000029
View details for PubMedID 22949701
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Ab initio kinetic Monte Carlo model of ionic conduction in bulk yttria-stabilized zirconia
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2012; 20 (6)
View details for DOI 10.1088/0965-0393/20/6/065006
View details for Web of Science ID 000308251800006
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Computing dislocation stress fields in anisotropic elastic media using fast multipole expansions
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2012; 20 (4)
View details for DOI 10.1088/0965-0393/20/4/045015
View details for Web of Science ID 000305477800015
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Dislocation dynamics simulation of Frank-Read sources in anisotropic alpha-Fe
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2012; 20 (4)
View details for DOI 10.1088/0965-0393/20/4/045022
View details for Web of Science ID 000305477800022
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Contribution of dislocation dipole structures to the acoustic nonlinearity
JOURNAL OF APPLIED PHYSICS
2012; 111 (7)
View details for DOI 10.1063/1.3699362
View details for Web of Science ID 000303282403001
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Stress-driven migration of simple low-angle mixed grain boundaries
ACTA MATERIALIA
2012; 60 (3): 1395-1407
View details for DOI 10.1016/j.actamat.2011.11.032
View details for Web of Science ID 000301157900061
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Plasticity of metal nanowires
JOURNAL OF MATERIALS CHEMISTRY
2012; 22 (8): 3277-3292
View details for DOI 10.1039/c2jm13682a
View details for Web of Science ID 000299695400001
- Molecular Dynamics Comprehensive Nuclear Materials edited by Konings, R. Elsevier. 2012: 249-265
- Molecular Dynamics Comprehensive Nuclear Materials edited by Konings, R. J., M. Elsevier. 2012: 249-265
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Equilibrium shape of dislocation shear loops in anisotropic alpha-Fe
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2011; 19 (6)
View details for DOI 10.1088/0965-0393/19/6/065006
View details for Web of Science ID 000294048100006
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Molecular dynamics simulations of gold-catalyzed growth of silicon bulk crystals and nanowires
JOURNAL OF MATERIALS RESEARCH
2011; 26 (17): 2199-2206
View details for DOI 10.1557/jmr.2011.155
View details for Web of Science ID 000296083100008
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Predicting the dislocation nucleation rate as a function of temperature and stress
JOURNAL OF MATERIALS RESEARCH
2011; 26 (18): 2335-2354
View details for DOI 10.1557/jmr.2011.275
View details for Web of Science ID 000296083600001
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Energy barrier for homogeneous dislocation nucleation: Comparing atomistic and continuum models
SCRIPTA MATERIALIA
2011; 64 (11): 1043-1046
View details for DOI 10.1016/j.scriptamat.2011.02.023
View details for Web of Science ID 000289607400012
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Entropic effect on the rate of dislocation nucleation
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2011; 108 (13): 5174-5178
Abstract
Dislocation nucleation is essential to our understanding of plastic deformation, ductility, and mechanical strength of crystalline materials. Molecular dynamics simulation has played an important role in uncovering the fundamental mechanisms of dislocation nucleation, but its limited timescale remains a significant challenge for studying nucleation at experimentally relevant conditions. Here we show that dislocation nucleation rates can be accurately predicted over a wide range of conditions by determining the activation free energy from umbrella sampling. Our data reveal very large activation entropies, which contribute a multiplicative factor of many orders of magnitude to the nucleation rate. The activation entropy at constant strain is caused by thermal expansion, with negligible contribution from the vibrational entropy. The activation entropy at constant stress is significantly larger than that at constant strain, as a result of thermal softening. The large activation entropies are caused by anharmonic effects, showing the limitations of the harmonic approximation widely used for rate estimation in solids. Similar behaviors are expected to occur in other nucleation processes in solids.
View details for DOI 10.1073/pnas.1017171108
View details for Web of Science ID 000288894800012
View details for PubMedID 21402933
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Dislocation junctions and jogs in a free-standing FCC thin film
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2011; 19 (2)
View details for DOI 10.1088/0965-0393/19/2/025002
View details for Web of Science ID 000287801400002
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The stability of Lomer-Cottrell jogs in nanopillars
SCRIPTA MATERIALIA
2011; 64 (6): 529-532
View details for DOI 10.1016/j.scriptamat.2010.11.037
View details for Web of Science ID 000286866200014
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Enhancing ionic conductivity of bulk single-crystal yttria-stabilized zirconia by tailoring dopant distribution
PHYSICAL REVIEW B
2011; 83 (5)
View details for DOI 10.1103/PhysRevB.83.052301
View details for Web of Science ID 000287358900001
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Dislocation contribution to acoustic nonlinearity: The effect of orientation-dependent line energy
JOURNAL OF APPLIED PHYSICS
2011; 109 (1)
View details for DOI 10.1063/1.3530736
View details for Web of Science ID 000286219300159
- Entropic Effect on the Rate of Dislocation Nucleation 2011
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Nanoscale patterning controls inorganic-membrane interface structure
NANOSCALE
2011; 3 (2): 391-400
Abstract
The ability to non-destructively integrate inorganic structures into or through biological membranes is essential to realizing full bio-inorganic integration, including arrayed on-chip patch-clamps, drug delivery, and biosensors. Here we explore the role of nanoscale patterning on the strength of biomembrane-inorganic interfaces. AFM measurements show that inorganic probes functionalized with hydrophobic bands with thicknesses complimentary to the hydrophobic lipid bilayer core exhibit strong attachment in the bilayer. As hydrophobic band thickness increases to 2-3 times the bilayer core the interfacial strength decreases, comparable to homogeneously hydrophobic probes. Analytical calculations and molecular dynamics simulations predict a transition between a 'fused' interface and a 'T-junction' that matches the experimental results, showing lipid disorder and defect formation for thicker bands. These results show that matching biological length scales leads to more intimate bio-inorganic junctions, enabling rational design of non-destructive membrane interfaces.
View details for DOI 10.1039/c0nr00486c
View details for Web of Science ID 000287363500006
View details for PubMedID 20931126
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Analysis of the elastic strain energy driving force for grain boundary migration using phase field simulation
SCRIPTA MATERIALIA
2010; 63 (11): 1049-1052
View details for DOI 10.1016/j.scriptamat.2010.07.034
View details for Web of Science ID 000282866700004
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Size and temperature effects on the fracture mechanisms of silicon nanowires: Molecular dynamics simulations
INTERNATIONAL JOURNAL OF PLASTICITY
2010; 26 (9): 1387-1401
View details for DOI 10.1016/j.ijplas.2010.02.001
View details for Web of Science ID 000281918700006
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Numerical tests of nucleation theories for the Ising models
PHYSICAL REVIEW E
2010; 82 (1)
Abstract
The classical nucleation theory (CNT) is tested systematically by computer simulations of the two-dimensional (2D) and three-dimensional (3D) Ising models with a Glauber-type spin flip dynamics. While previous studies suggested potential problems with CNT, our numerical results show that the fundamental assumption of CNT is correct. In particular, the Becker-Döring theory accurately predicts the nucleation rate if the correct droplet free energy function is provided as input. This validates the coarse graining of the system into a one dimensional Markov chain with the largest droplet size as the reaction coordinate. Furthermore, in the 2D Ising model, the droplet free energy predicted by CNT matches numerical results very well, after a logarithmic correction term from Langer's field theory and a constant correction term are added. But significant discrepancies are found between the numerical results and existing theories on the magnitude of the logarithmic correction term in the 3D Ising model. Our analysis underscores the importance of correctly accounting for the temperature dependence of surface energy when comparing numerical results and nucleation theories.
View details for DOI 10.1103/PhysRevE.82.011603
View details for Web of Science ID 000279941800008
View details for PubMedID 20866625
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Plasticity of metal wires in torsion: Molecular dynamics and dislocation dynamics simulations
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS
2010; 58 (7): 1011-1025
View details for DOI 10.1016/j.jmps.2010.04.010
View details for Web of Science ID 000279441700005
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Efficient computation of forces on dislocation segments in anisotropic elasticity
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2010; 18 (4)
View details for DOI 10.1088/0965-0393/18/4/045013
View details for Web of Science ID 000277087400013
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Atomistic simulations of surface segregation of defects in solid oxide electrolytes
ACTA MATERIALIA
2010; 58 (6): 2197-2206
View details for DOI 10.1016/j.actamat.2009.12.005
View details for Web of Science ID 000275511700028
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Validity of classical nucleation theory for Ising models
PHYSICAL REVIEW E
2010; 81 (3)
Abstract
While the classical nucleation theory (CNT) is widely used to predict the rate of first-order phase transitions, its validity has been questioned due to discrepancies with experiments. We systematically test the individual components of CNT by computer simulations of the Ising models and confirm its fundamental assumptions under a wide range of conditions ( h=0.01-0.13J , T=0.44-0.84Tc in two-dimensions and h=0.30-0.60J , T=0.48-0.62Tc in three dimensions). First, CNT accurately predicts the nucleation rate if the correct droplet free energy is provided. Furthermore, theoretical prediction of droplet free energy matches numerical results very well in the two-dimensional (2D) Ising model, if appropriate correction terms are added. This establishes the 2D Ising model as an important reference point where existing theories can predict nucleation rate accurately with no adjustable parameters.
View details for DOI 10.1103/PhysRevE.81.030601
View details for Web of Science ID 000276199300006
View details for PubMedID 20365686
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A gold-silicon potential fitted to the binary phase diagram
JOURNAL OF PHYSICS-CONDENSED MATTER
2010; 22 (5)
Abstract
We develop an empirical interatomic potential model for the gold-silicon binary system that is fitted to the experimental phase diagram. The model is constructed on the basis of the modified embedded-atom-method formalism and its binary phase diagram is computed by efficient free energy methods. The eutectic temperature and eutectic composition of the model match well with the experimental values. We expect the model to be useful for atomistic simulations of gold-catalyzed growth of silicon nanowires.
View details for DOI 10.1088/0953-8984/22/5/055401
View details for Web of Science ID 000273730300008
View details for PubMedID 21386339
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Kinetic Monte Carlo simulations of oxygen vacancy diffusion in a solid electrolyte: Computing the electrical impedance using the fluctuation-dissipation theorem
ELECTROCHEMISTRY COMMUNICATIONS
2010; 12 (2): 223-226
View details for DOI 10.1016/j.elecom.2009.11.031
View details for Web of Science ID 000274878400013
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Role of surface roughness in hysteresis during adhesive elastic contact
PHILOSOPHICAL MAGAZINE LETTERS
2010; 90 (12): 891-902
Abstract
In experiments that involve contact with adhesion between two surfaces, as found in atomic force microscopy or nanoindentation, two distinct contact force (P) vs. indentation-depth (h) curves are often measured depending on whether the indenter moves towards or away from the sample. The origin of this hysteresis is not well understood and is often attributed to moisture, plasticity or viscoelasticity. Here we report experiments that show that hysteresis can exist in the absence of these effects, and that its magnitude depends on surface roughness. We develop a theoretical model in which the hysteresis appears as the result of a series of surface instabilities, in which the contact area grows or recedes by a finite amount. The model can be used to estimate material properties from contact experiments even when the measured P-h curves are not unique.
View details for DOI 10.1080/09500839.2010.521204
View details for Web of Science ID 000283319100005
View details for PubMedID 21152108
- The Validity of Classical Nucleation Theory for Ising Models Physical Review E (Rapid Communications) 2010; 81: 030601
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Orientation-Dependent Plasticity in Metal Nanowires under Torsion: Twist Boundary Formation and Eshelby Twist
NANO LETTERS
2010; 10 (1): 139-142
Abstract
We show that the plastic deformation of nanowires under torsion can be either homogeneous or heterogeneous, regardless of size, depending on the wire orientation. Homogeneous deformation occurs when 110-oriented face-centered-cubic metal wires are twisted, leading to the nucleation of coaxial dislocations, analogous to the Eshelby twist mechanism. Heterogeneous deformation is predicted for 111 and 100 wires under torsion, localized at the twist boundaries. These simulations also reveal the detailed mechanisms of twist boundary formation from dislocation reactions.
View details for DOI 10.1021/nl903041m
View details for Web of Science ID 000273428700024
View details for PubMedID 20030357
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Modelling dislocations in a free-standing thin film
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2009; 17 (7)
View details for DOI 10.1088/0965-0393/17/7/075007
View details for Web of Science ID 000270055000008
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Improved modified embedded-atom method potentials for gold and silicon
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2009; 17 (7)
View details for DOI 10.1088/0965-0393/17/7/075008
View details for Web of Science ID 000270055000009
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Mechanics of Crystalline Nanowires
MRS BULLETIN
2009; 34 (3): 178-183
View details for Web of Science ID 000264325100014
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Energy of a Prismatic Dislocation Loop in an Elastic Cylinder
MATHEMATICS AND MECHANICS OF SOLIDS
2009; 14 (1-2): 192-206
View details for DOI 10.1177/1081286508092611
View details for Web of Science ID 000262418800015
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Dislocation dynamics simulations in a cylinder
IOP PUBLISHING LTD. 2009
View details for DOI 10.1088/1757-899X/3/1/012007
View details for Web of Science ID 000309682300007
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Comparison of thermal properties predicted by interatomic potential models
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2008; 16 (8)
View details for DOI 10.1088/0965-0393/16/8/085005
View details for Web of Science ID 000260759100005
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Torsion and bending periodic boundary conditions for modeling the intrinsic strength of nanowires
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS
2008; 56 (11): 3242-3258
View details for DOI 10.1016/j.jmps.2008.07.005
View details for Web of Science ID 000260946700009
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Comparing the strength of f.c.c. and b.c.c. sub-micrometer pillars: Compression experiments and dislocation dynamics simulations
ELSEVIER SCIENCE SA. 2008: 21-25
View details for DOI 10.1016/j.msea.2007.08.093
View details for Web of Science ID 000259844800004
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Surface-controlled dislocation multiplication in metal micropillars
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2008; 105 (38): 14304-14307
Abstract
Understanding the plasticity and strength of crystalline materials in terms of the dynamics of microscopic defects has been a goal of materials research in the last 70 years. The size-dependent yield stress observed in recent experiments of submicrometer metallic pillars provides a unique opportunity to test our theoretical models, allowing the predictions from defect dynamics simulations to be directly compared with mechanical strength measurements. Although depletion of dislocations from submicrometer face-centered-cubic (FCC) pillars provides a plausible explanation of the observed size-effect, we predict multiplication of dislocations in body-centered-cubic (BCC) pillars through a series of molecular dynamics and dislocation dynamics simulations. Under the combined effects from the image stress and dislocation core structure, a dislocation nucleated from the surface of a BCC pillar generates one or more dislocations moving in the opposite direction before it exits from the surface. The process is repeatable so that a single nucleation event is able to produce a much larger amount of plastic deformation than that in FCC pillars. This self-multiplication mechanism suggests a need for a different explanation of the size dependence of yield stress in FCC and BCC pillars.
View details for DOI 10.1073/pnas.0806118105
View details for Web of Science ID 000259592400016
View details for PubMedID 18787126
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Quantum entanglement of formation between qudits
PHYSICAL REVIEW A
2008; 77 (5)
View details for DOI 10.1103/PhysRevA.77.052312
View details for Web of Science ID 000257023900050
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Computing image stress in an elastic cylinder
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS
2007; 55 (10): 2027-2054
View details for DOI 10.1016/j.jmps.2007.03.007
View details for Web of Science ID 000250690200001
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Electronic structure calculations in a uniform magnetic field using periodic supercells
JOURNAL OF COMPUTATIONAL PHYSICS
2007; 226 (2): 1310-1331
View details for DOI 10.1016/j.jcp.2007.05.022
View details for Web of Science ID 000250209700007
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Enabling strain hardening simulations with dislocation dynamics
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2007; 15 (6): 553-595
View details for DOI 10.1088/0965-0393/15/6/001
View details for Web of Science ID 000249392800001
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Brittle and ductile fracture of semiconductor nanowires - molecular dynamics simulations
PHILOSOPHICAL MAGAZINE
2007; 87 (14-15): 2169-2189
View details for DOI 10.1080/14786430701222739
View details for Web of Science ID 000246814700008
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A hybrid method for computing forces on curved dislocations intersecting free surfaces in three-dimensional dislocation dynamics
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
2006; 14 (7): 1139-1151
View details for DOI 10.1088/0965-0393/14/7/003
View details for Web of Science ID 000242383700003
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Geometric aspects of the ideal shear resistance in simple crystal lattices
PHILOSOPHICAL MAGAZINE
2006; 86 (25-26): 3847-3859
View details for DOI 10.1080/14786430600643282
View details for Web of Science ID 000238567000005
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Dislocation multi-junctions and strain hardening
NATURE
2006; 440 (7088): 1174-1178
Abstract
At the microscopic scale, the strength of a crystal derives from the motion, multiplication and interaction of distinctive line defects called dislocations. First proposed theoretically in 1934 (refs 1-3) to explain low magnitudes of crystal strength observed experimentally, the existence of dislocations was confirmed two decades later. Much of the research in dislocation physics has since focused on dislocation interactions and their role in strain hardening, a common phenomenon in which continued deformation increases a crystal's strength. The existing theory relates strain hardening to pair-wise dislocation reactions in which two intersecting dislocations form junctions that tie the dislocations together. Here we report that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed 'multi-junctions'. We first predict the existence of multi-junctions using dislocation dynamics and atomistic simulations and then confirm their existence by transmission electron microscopy experiments in single-crystal molybdenum. In large-scale dislocation dynamics simulations, multi-junctions present very strong, nearly indestructible, obstacles to dislocation motion and furnish new sources for dislocation multiplication, thereby playing an essential role in the evolution of dislocation microstructure and strength of deforming crystals. Simulation analyses conclude that multi-junctions are responsible for the strong orientation dependence of strain hardening in body-centred cubic crystals.
View details for DOI 10.1038/nature04658
View details for Web of Science ID 000237080000041
View details for PubMedID 16641992
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A non-singular continuum theory of dislocations
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS
2006; 54 (3): 561-587
View details for DOI 10.1016/j.jmps.2005.09.005
View details for Web of Science ID 000236132800005
- Computer Simulations of Dislocations Oxford University Press. 2006
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Stochastic simulation of dislocation glide in tantalum and Ta-based alloys
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS
2005; 53 (6): 1223-1247
View details for DOI 10.1016/j.jmps.2005.01.003
View details for Web of Science ID 000229272400001
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Adaptive importance sampling Monte Carlo simulation of rare transition events
JOURNAL OF CHEMICAL PHYSICS
2005; 122 (7)
Abstract
We develop a general theoretical framework for the recently proposed importance sampling method for enhancing the efficiency of rare-event simulations [W. Cai, M. H. Kalos, M. de Koning, and V. V. Bulatov, Phys. Rev. E 66, 046703 (2002)], and discuss practical aspects of its application. We define the success/fail ensemble of all possible successful and failed transition paths of any duration and demonstrate that in this formulation the rare-event problem can be interpreted as a "hit-or-miss" Monte Carlo quadrature calculation of a path integral. The fact that the integrand contributes significantly only for a very tiny fraction of all possible paths then naturally leads to a "standard" importance sampling approach to Monte Carlo (MC) quadrature and the existence of an optimal importance function. In addition to showing that the approach is general and expected to be applicable beyond the realm of Markovian path simulations, for which the method was originally proposed, the formulation reveals a conceptual analogy with the variational MC (VMC) method. The search for the optimal importance function in the former is analogous to finding the ground-state wave function in the latter. In two model problems we discuss practical aspects of finding a suitable approximation for the optimal importance function. For this purpose we follow the strategy that is typically adopted in VMC calculations: the selection of a trial functional form for the optimal importance function, followed by the optimization of its adjustable parameters. The latter is accomplished by means of an adaptive optimization procedure based on a combination of steepest-descent and genetic algorithms.
View details for DOI 10.1063/1.1844352
View details for Web of Science ID 000227140000006
View details for PubMedID 15743217
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Kinetic Monte Carlo method for dislocation migration in the presence of solute
PHYSICAL REVIEW B
2005; 71 (1)
View details for DOI 10.1103/PhysRevB.71.014106
View details for Web of Science ID 000226735100049
- Modelling Dislocations using a Periodic Supercell Handbook of Materials Modelling edited by Yip, S. Springer. 2005
- Modeling Dislocations using a Periodic Supercell Handbook of Materials Modelling edited by Yip, S. Springer. 2005
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Mobility laws in dislocation dynamics simulations
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
2004; 387: 277-281
View details for DOI 10.1016/j.msea.2003.12.085
View details for Web of Science ID 000226042400059
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Core energy and Peierls stress of a screw dislocation in bcc molybdenum: A periodic-cell tight-binding study
PHYSICAL REVIEW B
2004; 70 (10)
View details for DOI 10.1103/PhysRevB.70.104113
View details for Web of Science ID 000224209300032
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Ab initio calculations in a uniform magnetic field using periodic supercells
PHYSICAL REVIEW LETTERS
2004; 92 (18)
Abstract
We present a formulation of ab initio electronic structure calculations in a finite magnetic field, which retains the simplicity and efficiency of techniques widely used in first principles molecular dynamics simulations, based on plane-wave basis sets and Fourier transforms. In addition we discuss results obtained with this method for the energy spectrum of interacting electrons in quantum wells, and for the electronic properties of dense fluid deuterium in a uniform magnetic field.
View details for DOI 10.1103/PhysRevLett.92.186402
View details for Web of Science ID 000221277900044
View details for PubMedID 15169514
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Dynamic transitions from smooth to rough to twinning in dislocation motion
NATURE MATERIALS
2004; 3 (3): 158-163
Abstract
The motion of dislocations in response to stress dictates the mechanical behaviour of materials. However, it is not yet possible to directly observe dislocation motion experimentally at the atomic level. Here, we present the first observations of the long-hypothesized kink-pair mechanism in action using atomistic simulations of dislocation motion in iron. In a striking deviation from the classical picture, dislocation motion at high strain rates becomes rough, resulting in spontaneous self-pinning and production of large quantities of debris. Then, at still higher strain rates, the dislocation stops abruptly and emits a twin plate that immediately takes over as the dominant mode of plastic deformation. These observations challenge the applicability of the Peierls threshold concept to the three-dimensional motion of screw dislocations at high strain rates, and suggest a new interpretation of plastic strength and microstructure of shocked metals.
View details for DOI 10.1038/nmat1072
View details for Web of Science ID 000189345100017
View details for PubMedID 14991017
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Massively-parallel dislocation dynamics simulations
IUTAM SYMPOSIUM ON MESOSCOPIC DYNAMICS OF FRACTURE PROCESS AND MATERIALS STRENGTH
2004; 115: 1-11
View details for Web of Science ID 000222604600001
- Dislocation Core Effects on Mobility Dislocations in Solids edited by Nabarro, F. R., N., Hirth, J., P. North-Holland Pub. 2004: 1
- Scalable Line Dynamics in ParaDiS, Conference on High Performance Networking and Computing 2004
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Dislocation image stresses at free surfaces by the finite element method
THIN FILMS-STRESSES AND MECHANICAL PROPERTIES X
2004; 795: 29-33
View details for Web of Science ID 000189484000005
- Dislocation Core Effects on Mobility Dislocations in Solids North-Holland Pub. 2004: 1-80
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Modeling of dislocation-grain boundary interactions in FCC metals
JOURNAL OF NUCLEAR MATERIALS
2003; 323 (2-3): 281-289
View details for DOI 10.1016/j.jnucmat.2003.08.008
View details for Web of Science ID 000187074300017
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Anomalous dislocation multiplication in FCC metals
PHYSICAL REVIEW LETTERS
2003; 91 (2)
Abstract
Direct atomistic simulations of dislocation multiplication in fcc aluminum reveal an unexpected mechanism, in which a Frank-Read source emits dislocations with Burgers vectors different from that of the source itself. The mechanism is traced to a spontaneous nucleation of partial dislocation loops within the stacking fault. Understanding and a quantitative description of this unusual process are achieved through the development of a continuum model for dislocation nucleation based on the coarse-grained dislocation dynamics approach and a minimal amount of atomistic input.
View details for DOI 10.1103/PhysRevLett.91.025503
View details for Web of Science ID 000184086000023
View details for PubMedID 12906487
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Periodic image effects in dislocation modelling
PHILOSOPHICAL MAGAZINE
2003; 83 (5): 539-567
View details for DOI 10.1080/0141861021000051109
View details for Web of Science ID 000181813100001
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Atomistic measures of materials strength and deformation
COMPUTATIONAL MATERIALS SCIENCE
2003; 187: 359-387
View details for Web of Science ID 000189488000018
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Importance sampling of rare transition events in Markov processes
PHYSICAL REVIEW E
2002; 66 (4)
Abstract
We present an importance sampling technique for enhancing the efficiency of sampling rare transition events in Markov processes. Our approach is based on the design of an importance function by which the absolute probability of sampling a successful transition event is significantly enhanced, while preserving the relative probabilities among different successful transition paths. The method features an iterative stochastic algorithm for determining the optimal importance function. Given that the probability of sampling a successful transition event is enhanced by a known amount, transition rates can be readily computed. The method is illustrated in one- and two-dimensional systems.
View details for DOI 10.1103/PhysRevE.66.046703
View details for Web of Science ID 000179176300135
View details for PubMedID 12443376
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Nodal effects in dislocation mobility
PHYSICAL REVIEW LETTERS
2002; 89 (11)
Abstract
We show that, contrary to the prevailing perception, dislocations can become more mobile by zipping together to form junctions. In a series of direct atomistic simulations, the critical stress to move a junction network in a [110] plane of bcc molybdenum is found to be always smaller ( approximately 50%) than that required to move isolated dislocations. Our data support a previously proposed hypothesis about the nature of anomalous slip in bcc transition metals, yet offer a different atomistic mechanism for conservative motion of screw dislocation networks. The same data suggest a hierarchy of motion mechanisms in which lower-dimensional crystal imperfections control the rate of sliding along the low-angle twist boundaries.
View details for DOI 10.1103/PhysRevLett.89.115501
View details for Web of Science ID 000177676400015
View details for PubMedID 12225147
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Molecular dynamics simulations of motion of edge and screw dislocations in a metal
COMPUTATIONAL MATERIALS SCIENCE
2002; 23 (1-4): 111-115
View details for Web of Science ID 000175870500015
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Kinetic Monte Carlo approach to modeling dislocation mobility
COMPUTATIONAL MATERIALS SCIENCE
2002; 23 (1-4): 124-130
View details for Web of Science ID 000175870500017
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Dislocation motion in BCC metals by molecular dynamics
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
2001; 309: 160-163
View details for Web of Science ID 000169044600035
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Point defect interaction with dislocations in silicon
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
2001; 309: 129-132
View details for Web of Science ID 000169044600028
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Kinetic Monte Carlo modeling of dislocation motion in BCC metals
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
2001; 309: 270-273
View details for Web of Science ID 000169044600056
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Anisotropic elastic interactions of a periodic dislocation array
PHYSICAL REVIEW LETTERS
2001; 86 (25): 5727-5730
Abstract
A method for calculating the anisotropic elastic energy of a dislocation dipole in a periodic cell is derived in which the infinite image summation is absolutely convergent. The core energy of a screw dislocation in Si, extracted from atomistic simulation, is shown to be manifestly system size invariant. Existence of special cell geometry where complete cancellation of elastic interactions occurs is demonstrated.
View details for Web of Science ID 000169373000022
View details for PubMedID 11415343
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Parameter-free modelling of dislocation motion: the case of silicon
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES
2001; 81 (5): 1257-1281
View details for Web of Science ID 000168757700015
- Commentary on Atomistic Simulations of Materials Strength and Deformation: Prospects for Mechanistic Insights, Materials Science for the 21st Century 2001; A: 220-233
- Atomistic and Mesoscale Modeling of Dislocation Mobility PhD Thesis Massachusetts Institute of Technology. 2001
- Periodic Boundary Conditions for Dislocation Dynamics Simulations in Three Dimensions 2001
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Minimizing boundary reflections in coupled-domain simulations
PHYSICAL REVIEW LETTERS
2000; 85 (15): 3213-3216
Abstract
We propose a time-dependent boundary condition coupling an atomistic simulation system to linear surroundings such that reflection of elastic waves across the boundary is minimized. Interdomain interactions expressed in terms of memory kernel functions within linear-response theory are treated in a natural dynamical manner, albeit numerically. The approach is shown to give significantly reduced phonon reflections at the domain boundaries relative to existing coupling methods. In addition, we demonstrate that the framework is also effective in the context of static relaxation of displacement fields associated with embedded inhomogeneities.
View details for Web of Science ID 000089807800037
View details for PubMedID 11019304
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Efficient free-energy calculations by the simulation of nonequilibrium processes
COMPUTING IN SCIENCE & ENGINEERING
2000; 2 (3): 88-96
View details for Web of Science ID 000086632500020
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Intrinsic mobility of a dissociated Dislocation in silicon
PHYSICAL REVIEW LETTERS
2000; 84 (15): 3346-3349
View details for Web of Science ID 000086404500033
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Vacancy interaction with dislocations in silicon: The shuffle-glide competition
PHYSICAL REVIEW LETTERS
2000; 84 (10): 2172-2175
View details for Web of Science ID 000085650100031
- Efficient Free-Energy Calculations by the Simulation of Nonequilibrium Processes Computing in Science and Engineering 2000; 2: 88
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Dynamics of dissociated dislocations in Si: A micro-meso simulation methodology
MULTISCALE MODELLING OF MATERIALS
1999; 538: 69-75
View details for Web of Science ID 000080728000007
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Kinetic Monte Carlo method for dislocation glide in silicon
JOURNAL OF COMPUTER-AIDED MATERIALS DESIGN
1999; 6 (2-3): 175-183
View details for Web of Science ID 000088287400011
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Kink asymmetry and multiplicity in dislocation cores
PHYSICAL REVIEW LETTERS
1997; 79 (25): 5042-5045
View details for Web of Science ID 000071096100026