We have developed a number of simulation techniques in the realm of accelerated molecular dynamics (MD) and enhanced sampling, in particular force bias Monte Carlo (fbMC) simulations and collective variable-driven hyperdynamics (CVHD) simulations.

With force-bias Monte Carlo (fbMC) techniques, larger atomic displacements can be achieved than generally possible in MD.  The main successful application of fbMC is due to its ability to relax a system much faster than MD, which makes it very useful in conjunction with MD.  A typical use is the modelling of chemical vapor deposition (CVD) processes on a surface, in which impacts by gas-phase species can be performed using MD, and the subsequent relaxation of the surface by fbMC.  This allows to use higher fluxes, effectively extending the time scale of the simulation.  The method is implemented in LAMMPS and ADF .

The collective variable-driven hyperdynamics (CVHD) method is an accelerated molecular dynamics technique based on both hyperdynamics and metadynamics. In hyperdynamics, a bias is added to the potential energy of the system to destabilize minima and consequently accelerate transitions to other minima (such as chemical reactions, conformational changes, diffusion events, etc.).  To create a generic hyperdynamics implementation, CVHD borrows the concept of collective variables from metadynamics.  Moroever, the CVHD bias is designed to be self-learning, in order to match the current demands of the system while not requiring a priori knowledge about the system.

The CVHD method has already been succesfully applied to a wide variety of problems, namely surface diffusion, reaching time scales up to 500 seconds, folding of a model chain-like polymer at 300 K over a time of about 6 µs, catalytic decomposition of a CH4 molecule on Ni(111) at 800 K, reaching the millisecond time scale, and pyrolysis and combustion of n-dodecane, at time scales up to 40 seconds.

More information on the CVHD method and instructions to download and apply the code can be found here.