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Atomistic materials simulations in PRISM

Atomistic simulations of contact physics Alejandro Strachan Materials Engineering strachan@purdue.edu. Atomistic materials simulations in PRISM. Develop first principles-based constitutive relationships and provide atomic level insight for coarse grain models.

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Atomistic materials simulations in PRISM

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  1. Atomistic simulations of contact physicsAlejandro StrachanMaterials Engineering strachan@purdue.edu

  2. Atomistic materials simulations in PRISM Develop first principles-based constitutive relationships and provide atomic level insight for coarse grain models • Identify and quantify the molecular level mechanisms that govern performance, reliability and failure of PRISM device using: • Ab initio simulations • Large-scale MD simulations

  3. PRISM multi-physics integration • Trapped charges in dielectric Predictions Electronic processes Validation Experiments: Microstructure evolution, device performance & reliability PRISM Device simulation MPM & FVM • Elastic, plastic deformation, failure Micromechanics • Defect nucleation & mobility in dielectric • Fluid damping Fluid dynamics • Temperature & species • Dislocation and vacancy nucleation & mobility in metal Atomistics Thermal and mass transport • Fluid-solid interactions • Thermal & electrical conductivity Input Experiments: Surface roughness, composition, defect densities, grain size and texture

  4. Atomistic modeling of contact physics Interatomic potentials Implicit description of electrons How: classical MD with ab initio-based potentials Size: 200 M to 1.5 B atoms Time scales: nanoseconds Predictions: Role of initial microstructure & surface roughness, moisture and impact velocity on: Force-separation relationships (history dependent) Generation of defects in metal & roughness evolution Mechanical response: Generation of defects in dielectric (dielectric charging) Thermal role of electrons in metals Current crowding and Joule Heating Electronic properties: Surface chemical reactions Chemistry: Main Challenges

  5. Atomistic modeling of contact physics: II Smaller scale (0.5 – 2 M atom) and longer time (100 ns) simulations to uncover specific physics: • Mobility of dislocations in metal, • Interactions with other defects (e.g. GBs) • Link to phase fields • Surface chemical reactions • Reactive MD using ReaxFF • Defects in semiconductor • Mobility and recombination • Role of electric charging • Fluid-solid interaction: • Interaction of single gas molecule with surface (accommodation coefficients) for rarefied gas regime

  6. Obtaining surface separation-force relationships • Contact closing and opening simulation • 200 M to 1.5 billion atoms – nanoseconds • (1 billion atom for 1 nanosecond ~ 1 day on a petascale computer) • Characterize effect of: • Impact velocities (4 values) • Moisture (4 values) • Applied force and stress (2 values) • Surface roughness • Peak to peak distance (2) and RMS (2) • Presence of a grain boundary (4 runs) 16 runs 4 runs 4 runs 4 runs 28 runs

  7. Upscaling MD to: fluid dynamics Given a distribution of incident momenta characterize the distribution of reflected momenta: Accommodation coefficients: pi Fluid FVM models use accommodation coefficients from MD and predict incident distribution Role of temperature and surface moisture on accommodation coefficients

  8. Upscaling MD to: electronic processes • Defect formation energies • Equilibrium concentration • Formation rates if temperature increases • Impact generated defects • Characterize their energy and mobility as a function of temperature • Predict the distribution non-equilibrium defects • Characterize energy level of defects • SeqQuest

  9. Upscaling MD to: micromechanics • Elastic constants • Vacancy formation energy and mobility • Bulk and grain boundaries • Dislocation core energies • Screw and edge • Dislocation nucleation energies • At grain boundaries, metal/oxide interface • Nucleation under non-equilibrium conditions (impact) • Dislocation mobility and cross slip • Interaction of dislocations with defects • Solute atoms and grain boundaries Upscaling MD to: thermals • Thermal conductivity of each component • Interfacial thermal resistivity • Role of closing force, moisture and temperature

  10. MD simulations: challenges • Accurate interatomic potentials • Start with state-of-the-art • Parameterize using ab initio calculations (ReaxFF, MEAM) • Incorporate thermal and transport role of electrons • Accurate description of thermal transport and Joule heating • Extend new method for dynamics with implicit degrees of freedom - Strachan and Holian, Phys. Rev. Lett. (2005)

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