A Multibox Splitting Scheme: Robust Approximation For ab Initio Molecular Dynamics

In this work, the multibox (M-box) simulation scheme is introduced, which can be considered as a generalization of the QM/MM scheme for multifragment (molecular) systems. This scheme exploits the natural locality of multifragment molecular-based systems by mapping the system into force-coupled block subspaces. Where defined in this way, the entire system can be fully modeled under a quantum mechanical force field. This allows the description of each subspace explicitly by means of a robust electronic structure theory without the requirement for large computational resources. An adequate block-to-block coupling by means of shared subsystem fragments is applied to preserve the long-distance structural correlation in the system during a molecular dynamic (MD) simulation. Since electronic structure descriptions play a central role in the formulation of several parametric models for charge or energy transport, we expect that this space-time correlated scheme can become a reliable computational tool for charge/energy transport/transfer applications. The efficiency of the method is demonstrated by performing statistical and time-resolved analysis using both the multifragment box and full ab initio approaches. We illustrate the method using as examples the melting process of a one-dimensional benzene chain (weak interaction situation) and NVE dynamics for the CnHn polymeric chain (strong interaction situation). We also have extended the threshold of applicability of our model, demonstrating how it can cope with MD simulation with more complex systems and processes.