Summer School on Computational Materials Science
University of Illinois, Urbana-Champaign


Accelerated Molecular Dynamics Methods

Tim Germann - - Los Alamos National Laboratory

Outline of Lecture

  1. Background
    1. Rare event examples: epitaxial growth, radiation damage - e.g. plutonium aging due to self-irradiation, ...
    2. Pitfalls of KMC: concerted multiatom mechanisms, unconventional crystal structures or grain boundary diffusion, ...
    3. One possibility: Henkelman-Jonsson saddle-point enumeration + KMC Seek MD acceleration technique(s) w/o biasing the dynamics
  2. Hyperdynamics
    1. Basic idea: boost PES in wells w/o affecting saddle points Mathematical justification (assuming TST) & definition of an accelerated time
    2. Demonstration on model system(s) using simple boost functions
    3. More sophisticated boost functions
    4. Application to more complex systems
    5. Unsolved problems: extension to systems with low barriers (or a range of barriers, e.g. glasses, liquids, proteins)
  3. Related approaches: temperature accelerated dynamics
    1. Basic idea: increase simulation temperature to find neighboring saddles, but reject transitions until low-temperature path can be accepted
    2. Mathematical justification (assuming harmonic TST)
    3. Demonstration on model system(s)
  4. Related approaches: parallel replica dynamics
    1. Basic idea: independent realization of system on each processor to explore phase space more rapidly; first processor to find escape pathway is accepted
    2. Mathematical justification (assuming infrequent events)
    3. Demonstration on model system(s)
    4. Brownian Monte Carlo
  5. Combining II and IV -> parallel replica hyperdynamics
    1. Multiplicative boost achieved
    2. Example: epitaxial growth of Cu/Cu(100) on 1000 procs -> 0.3 s
  6. Outlook & Prospects
  7. Lab
    1. Will focus on *'d topics; vary boost function, system size and complexity (e.g. single adatom diffusion vs. islands with both low and high barriers) to demonstrate where hyperMD works well and where it runs into difficulties.

Background Article

"A method for accelerating the molecular dynamics simulation of infrequent events", A. F. Voter, J. Chem. Phys. 106 4665 (1997).

Lecture 1

Accelerated Molecular Dynamics
  Adobe PDF Slides - download (5,379 KB PDF)

Lab Materials

Lab Notes - PDF file (26.5 KB) - lab-notes.pdf

  Lab Source - TAR file (36.5 KB) - lab-source.tar


Last Updated July 19, 2001
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