Theory and simulation of materials: some recent developments in research

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Theory and simulation of materials some recent
developments inresearch teaching

• Adrian Sutton
• Department of Physics, Imperial College London

University of Liverpool January 23, 2009
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Theory and simulation

• Recent research
• irradiation damage in metals
• interfaces
• Education
• postgraduate
• undergraduate

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Role of electrons in irradiation damage

• 14 MeV neutrons in a fusion reactor
• Local high temperature for ? 1ns
• Recrystallization
• Vacancies cluster ? dislocation loops
• hardening, possibly embrittlement
• Defect population affected by cooling rate
• Hot nuclei transfer energy to electrons
• Defect distribution strongly influenced by
  excited electrons

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Semi-classical molecular dynamics

• Classical ions F ma
• Quantum mechanical electrons
• Quantum Liouville equation
• Electrons may become excited
• Degree of electronic excitation calculated
• Influence on atomic dynamics fully captured

• J. le Page, D.R. Mason and W.M.C. Foulkes 2008,
  J. Phys. Cond. Matt. 20, 125212
• D.R. Mason et al. 2007, J. Phys. Cond. Matt.
  19, 436209

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Excitation as temperature rise
Electronic occupations
Energy transfer
Atoms displaced gt 0.1A
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Energy transfer as function of PKA direction

• Higher effective damping for lt110gt RCS

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Ion Channelling

• 1MeV ion, e hopping full Coulombic e-e
  interactions

104801 atoms
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Channelling
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The team

• Daniel Mason
• Chris Race
• Jonathan LePage
• Mike Finnis
• Matthew Foulkes
• Andrew Horsfield
• APS
• Funding EPSRC Materials Modelling Initiative

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Orderly and disorderly behaviour at interfaces
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Are GBs in pure Si disordered at 0K?

• GB structure calculated by (a) energy
  minimization and (b) simulated annealing
• (a) is ordered,
• (b) is disordered
• (b) is the lower energy structure
• P. Keblinski, S.R. Phillpot, D. Wolf and H.
  Gleiter,
• Phys. Rev. Lett. 77, 2965 (1996)

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Experimental results (001) twist GBs

• Narrow cusps in GB energy at ?25,13,17 and 5

A. Otsuki Interf. Sci. 9, 293 (2001)
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Our procedure

• Create an ideal twist GB
• Remove ?N atoms close to GB by random selection
• Melt GB region
• Quench from 2000 K down to 800 K at a rate of 50
  K/ns by molecular dynamics using Tersoff III
  potential

1.
2.
3.
4.
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?25 ?N47

• Misorientation angle ??16?
• Minimum energy structure for ?25
• GB energy 835 mJ/m2
• Regular network of
• 1/2lt110gt screw dislocations
• Structural units A and B at the intersection of
  the screw dislocations
• p2 space group

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Structural units
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Influence of ?N
?N29 Disordered High GB energy and large
strain Coordination defects
?N47 Ordered Low energy and no
coordination defects Screw dislocation network
visible
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?13 ?N21

• Misorientation angle ??23?
• Minimum energy boundary for ?13
• GB energy 866 mJ/m2
• Regular network of 1/2lt110gt screw dislocations
• A units at screw dislocation intersections
• Corrugated profile

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?5 ?N7

• Misorientation angle ?37?
• Minimum energy structure
• comprising one primitive cell
• GB energy 1108 mJ/m2
• A and B units as in ?25
• No coordination defects
• Space group p2

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Validation using DFT
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disorderly vs. orderly

• Minimum energy structure
• for ? 29 obtained by
• Keblinski et al. (1996)
• Disordered
• GB energy (SW)
• 1300 - 1340 mJ/m2

• Minimum energy structure obtained in
• this work for ? 29, ?N47
• Complex structure but ordered
• GB energy (SW) 1109 mJ/m2

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Movie of ? 5
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Summary of simulations of annealing up to Tm

• All 3 boundaries display some degree of order at
  all temperatures up to Tm no premelting or
  transition to an amorphous layer
• There are fluctuations in the arrangements and
  types of structural units at temperatures up to
  0.8 Tm
• Above 0.8 Tm fluctuations temporarily disorder
  the structural units in addition to effecting
  transitions between different types of structural
  units.

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A grand challenge

• The need for grand canonical simulations of
  interfaces
• Crucially dependent on good simple models of
  atomic interactions
• Use DFT for validation not prediction IN
  GENERAL configurational phase spaces of
  interfaces are far too complex for DFT

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The team

• Sebastian von Alfthan
• Peter Haynes
• Kimmo Kaski
• APS

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Doctoral Training Centre Theory and simulation
of materials
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The need for a DTC on TSM

• International criticism about British PhDs
• Decline of theoretical content of Materials
  degrees
• Decline of Materials content of Physics degrees
• Industrial need, especially with new nuclear
  build
• (but also other technologies for producing
  energy, telecommunications, aerospace and land
  transportation, storage processing and
  transmission of information, healthcare, security
  and defence)
• TSM is needed to
• guide selection of materials
• optimize design and performance,
• predict long-time behaviour and avoid failures
• think the unthinkable metamaterials

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The students we want to recruit

• 1st class honours degree in
• Physics
• Engineering subjects including Materials
• Chemistry
• Interested in developing and applying theory
• that makes a difference
• Open minded, interested in other disciplines
• Computation, writing major programs, often in
  teams
• Interested in working with experimentalists
• Interested in working with industry

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10 EPSRC-funded studentships p.a.

• Usual eligibility rules regarding nationality
  apply
• 4-year degree
• MSc in first year based on course work summer
  project
• Research project from years 2-4
• Need 60 to transfer to MPhil
• Transfer from MPhil to PhD at end of 2nd year
• Overseas students welcome subject to funding
• Maximum cohort size 25
• Limited places available for students wishing to
  do MSc only.
• Code F3U5 Theory and Simulation of Materials
• 1 year only MSc
• 4 years MSc PhD

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1st year MSc on TSM

• 20 staff in 4 Departments of Chemistry,
  Materials, Mechanical Engineering, and Physics
  involved in DTC
• 6 core courses
• 2 options
• Problem and computational classes
• Summer research project
• Continuous assessment and exams
• Cohort mentor scheme
• Networking and social activities
• Unique course with a fundamental mathematical
  approach, praised nationally and internationally
  by academe and industry through more than 40
  letters of support.

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Core courses

• Mathematical and computational methods
• Equilibrium in materials
• Change in materials
• Electronic structure of materials
• Elasticity and microplasticity
• Methods of simulating materials from electrons to
  finite elements

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Option courses

• Methods of characterizing materials and their
  theoretical interpretation
• Advanced continuum theories of microstructural
  evolution
• Polymers and soft condensed matter physics
• Advanced continuum field theory of defects
• Strengthening mechanisms and fracture
• Advanced electronic structure of materials and
  metamaterials
• Continuum theory of static and dynamic plasticity
• Advanced techniques of materials simulation.

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PhD in years 2-4

• All research projects required to bridge length
  scales and/or time scales.
• Projects selected during first year, ranging
  across length and time scales in functional and
  structural materials
• Two supervisors, with expertise in adjacent
  length scales, often from different Departments.
• Residential DTC specific GSEPS transferable
  skills courses
• All research carried out in TYC
• Further course options available in yrs 2-4
• DTC activities throughout yrs 2-4 to maintain
  strong sense of cohort identity.

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Undergraduate education

• Preparing bid to HEFCE Strategic Development Fund
• Joint venture between Imperial and UCL
• 4-year degree in Physics with Theoretical
  Materials Physics
• 1st two years same as straight Physics degree
• Theoretical Materials Physics courses in 3rd and
  4th years
• Direct feed into DTC

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