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Atomistic simulations of contact physics Alejandro Strachan Materials Engineering [email protected] 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 simulations of contact physicsAlejandro StrachanMaterials Engineering [email protected]

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

PRISM multi-physics integration

  • Trapped charges in dielectric




Validation Experiments:

Microstructure evolution, device performance & reliability

PRISM Device simulation


  • Elastic, plastic deformation, failure


  • Defect nucleation & mobility in dielectric

  • Fluid damping



  • Temperature & species

  • Dislocation and vacancy nucleation & mobility in metal


Thermal and

mass transport

  • Fluid-solid interactions

  • Thermal & electrical conductivity

Input Experiments:

Surface roughness, composition, defect densities, grain size and texture

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


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


Main Challenges

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

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

Upscaling MD to: fluid dynamics

Given a distribution of incident momenta characterize the distribution of reflected momenta:

Accommodation coefficients:


Fluid FVM models use accommodation coefficients from MD and predict incident distribution

Role of temperature and surface moisture on accommodation coefficients

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

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

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)