Accelerated molecular dynamics of rare events using the local boost method

We present the local boost method for accelerating molecular-dynamics (MD) simulations of rare-event processes. To accelerate the dynamics, a bias potential is used to raise the potential energy in regions other than the transition states. This method reduces the number of MD rime steps spent simulating motion in the potential-energy minima, and allows long-time simulations to be run. Correct equilibrium and dynamical quantities are achieved by using a time increment based on the principles of importance sampling. Two different bias potentials are probed. Both bias potentials are based on the potential energies of individual atoms. In both cases, the bias potential is turned on (off) when the energy of an individual atom is below (above) a boosting threshold energy. Implementing this method requires only minor modification to a conventional MD code, and the associated computational overhead is negligible. We demonstrate the method by applying it to the diffusion of atoms on Lennard-Jones fcc(001) and fcc(111) surfaces. Both single and multiple boosting-threshold energies are employed in these studies. These results show that the local boost method with multiple-boosting thresholds holds significant promise for application in large-scale MD simulations.