Atomistic-based continuum multiscale modeling

Buehler et al. presented a preliminary study on formation of water from molecular oxygen and hydrogen using a series of atomistic simulations based on ReaxFF MD method.111 They described the dynamics of water formation at a Pt catalyst. By performing this series of studies, we obtain statistically meaningful trajectories that permit to derive the reaction rate constants of water formation. However, the method requires calibrations with either ab initio simulation results in order to correctly evaluate the energetics of OER on Pt. Thus, this method is system specific and less reliable than the ab initio methods and will not replace ab initio methods. Nevertheless, this work demonstrates that atomistic simulation to continuum description can be linked with the ReaxFF MD in a hierarchical multiscale model. 

Like other multiscale methods, atomistic-continuum methods require an accurate treatment of the coupling between different domains. In addition to these difficulties, they pose serious challenges for performing extensive simulations. The physical processes described by continuum equations and particle-based models impose inherently distinct demands on the computer architerture. While continuum mechanics and hydrodynamics, typically dealing with regular meshes, are characterized by moderate computations with stractured communications, atomistic simulations are characterized by intense computations and intense interprocessor communications. As a result, large-scale simulations of this sort require a balanced computer architecture in terms of memory bandwidth and interconnea bandwidth. 

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