Adaptive-boost molecular dynamics simulation of carbon diffusion in iron

Abstract

We have developed an accelerated molecular dynamics (MD) method to model atomic-scale rare events. In this method, a smooth histogram of collective variables is first estimated by canonical ensemble molecular dynamics calculations, and then a temperature-dependent boost potential is iteratively constructed to accelerate the MD simulation. This method not only allows us to observe the rare events but also to evaluate the profile of free energy and trial frequency along the reaction coordinate. We employed this method to study carbon diffusion in BCC iron and evaluated carbon's temperature-dependent diffusivity. The obtained diffusivities agree well with the experimental measurements. Even at low temperature for which no experimental data are available, the diffusivity can be evaluated accurately. Additionally, we study carbon diffusion inside edge dislocation core in BCC iron, and demonstrate the applicability of the method to rare events on a rugged free energy surface.

“Conjugate Channeling” Effect in Dislocation Core Diffusion: Carbon Transport in Dislocated BCC Iron

“…Because the binding energy of carbon with edge dislocation is 0.96 from our previous work [14], the carbon interstitial and a segment of the edge dislocation in fact form a co-diffusing “molecule” or a “complex” that undergoes random walk together under thermal fluctuations. The size of this “molecule” can be very roughly estimated as follows.…”

Effect of temperature on kinetic nanofriction of a Brownian adparticle

“…It is known that accelerated molecular dynamics (AMD) techniques are mainly used to study the diffusion systems with a deep potential energy trap [30]. In such systems, an object spends most of its time in vibrating at the bottom of a deep potential well, and hence a jump is a rare event.…”

Mechanism transition and strong temperature dependence of dislocation nucleation from grain boundaries: An accelerated molecular dynamics study

“…Because dislocation nucleation is a thermally activated rate-controlling process at finite temperature and is usually rate sensitive, the temperature and strain-rate sensitivities should be carefully studied at realistic time scales [14,15]. Thus in this study we accelerate the dislocation-nucleation events using adaptive-boost MD (ABMD) [16,17] and study the dislocation nucleation with atomic-level resolution at finite temperature, which offers opportunities for more comprehensive investigation of these processes arising from interfacial defects. Note that while the temperature and strain-rate dependences of dislocation nucle-ation from surfaces have been studied using both atomistic modeling [18] and experiments [4], those of dislocation nucleation from GBs have not been studied yet.…”