Time Acceleration Methods in Atomistic Simulations

Kristen Fichthorn
Pennsylvania State University

A complete understanding of morphological evolution in thin-film epitaxy involves understanding the integration of a large number of phenomena occurring over a wide range of time scales. A significant challenge in theory is to correctly capture this interplay. To this end, we developed [1] the Bond-Boost Method for accelerated MD simulations of rare events and recently [2] we extended this method to handle processes occurring on widely separated time scales. For example, in metal thin-film growth the atom diffusion along island edges can be orders of magnitude faster than adatom hopping on terraces. These fast, recurrent events can impose severe limitations on the achievable simulation time. In our method, we detect, on the fly, groups of recurrent states connected by small energy barriers and we modify the potential-energy surface locally to consolidate them into large, coarse states. In this way, fast motion between recurrent states is treated within an equilibrium formalism and dynamics can be simulated over the longer time scale of the slow events. We simulate cluster diffusion and the initial growth of Co on Cu(001) and explain various aspects of growth [3], contrasting our results to those found in our earlier kinetic Monte Carlo study of this system [4].

[1] R. A. Miron and K. A. Fichthorn, J. Chem. Phys. 119, 6210 (2003)
[2] R. A. Miron and K. A. Fichthorn, Phys. Rev. Lett. 93, 128301 (2004).
[3] R. A. Miron and K. A. Fichthorn, Phys. Rev. B 72, 035415 (2005).
[4] R. Pentcheva, K.A. Fichthorn, M. Scheffler, T. Bernhard, R. Pfandzelter, and H. Winter, Phys. Rev. Lett. 90, 076101 (2003).

Back to Workshop II: Multiscale Modeling in Condensed Matter and Materials Sciences, including Mini-Workshop: Time Acceleration Methods in Atomistic Simulations