PowerPoint Presentation Accelerated Molecular Dynamics Methods

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Hyperdynamics
A web-based presentation Arthur F.
Voter Theoretical Division Los Alamos National
Laboratory Los Alamos, New Mexico USA Work
supported by DOE/BES
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Infrequent-Event System
The system vibrates in 3-N dimensional basin many
times before finding an escape path. In
hyperdynamics, we partially fill in the basins
with a bias potential to cause the trajectory to
find an appropriate escape path more quickly.
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Hyperdynamics
Builds on umbrella-sampling techniques (e.g.,
Valleau 1970s) Assumptions - infrequent
events - transition state theory (no recrossings)

• Procedure
• design bias potential DV (zero at dividing
  surfaces)
• run thermostatted trajectory on the biased
  surface (VDV)
• accumulate hypertime as
• thyper SDtMDexpDV(R(t))/kBT
• - time converges on correct value in long-time
  limit (w/ vanishing relative error)

AFV, J. Chem. Phys. 106, 4665 (1997)
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Hyperdynamics bias potential
An extremely simple form flat bias potential
VDV
V

• M. M. Steiner, P.-A. Genilloud, and J. W.
  Wilkins, Phys. Rev. B 57, 10236 (1998).
• - no more expensive than normal MD (negative
  overhead(!))
• very effective for low-dimensional systems
• - diminishing boost factor for more than a few
  atoms.

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Hyperdynamics
Key challenge is designing a more general bias
potential that meets the requirements of the
derivation and is computationally efficient. A
few forms have been proposed and tested. Still a
subject of ongoing research our
group Fichthorn et al (Penn State) Wilkins et
al (Ohio State) Smith, Sanz-Navarro
(Loughborough) Stuart et al (Clemson) Fang and
Wang For a recent review of the progress,
see A.F. Voter, F. Montalenti, and T.C. Germann,
Ann. Revu. Mat. Res. 32, 321 (2002).
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