1. Diffusive Molecular Dynamics
Ju Li, Bill Cox, Tom Lenosky,
Ning Ma, Yunzhi Wang
Ohio State University

4. Traditional Molecular Dynamics
Traditional MD numerically integrates Newton’s equation of motion over 3N degrees of freedom, the atomic positions:
It is difficult to reach diffusive time scales using traditional MD due to timestep (~ ps / 100), which needs to resolve atomic vibrations.

5. Diffusive MD: The Idea Variational Gaussian Method
Lesar, Najafabadi and Srolovitz,
Phys. Rev. Lett. 63 (1989) 624.
DMD
ci: occupation probability
(vacancy, solutes)
Define mi for each atom,
to drive diffusion
Ferris wheel seen with long
camera exposure time

6. Variational Gaussian Method
VG free energy
true free energy
{xi,ai}

7. Comparison with Monte Carlo
Lesar, Najafabadi and Srolovitz,
Phys. Rev. Lett. 63 (1989) 624.

9. DMD thermodynamics
VG view
DMD view

10. DMD kinetics
nearest-neighbor network

14. DMD is atomistic realization of regular solution model, with gradient thermo, long-range elastic interaction, and short-range coordination interactions all included.
DMD kinetics is “solving Cahn-Hilliard equation on a moving atom grid”, with atomic spatial resolution, but at diffusive timescales.
The “quasi-continuum” version of DMD can be coupled to well-established diffusion-microelasticity equation solvers such as phase-field method.
No need to pre-build event catalog. Could be competitive against kinetic Monte Carlo.