  The study of ion transport in electrochemically active materials for energy
storage systems requires simulations on quantum- atomistic- and mesoscales. The
methods accessing these scales not only have to be effective but also well
compatible to provide a full description of the underlying processes. We
propose to adapt the Generalized Shadow Hybrid Monte Carlo (GSHMC) method to
atomistic simulation of ion intercalation electrode materials for batteries.
The method has never been applied to simulations in solid state chemistry but
it has been successfully used for simulation of biological macromolecules,
demonstrating better performance and accuracy than can be achieved with the
popular molecular dynamics (MD) method. It has been also extended to
simulations on meso-scales, making it even more attractive for simulation of
battery materials. We combine GSHMC with the dynamical Core-Shell model to
incorporate polarizability into the simulation and apply the new Modified
Adaptive Integration Approach, MAIA, which allows for a larger time step due to
its excellent conservation properties. Also, we modify the GSHMC method,
without losing its performance and accuracy, to reduce the negative effect of
introducing a shell mass within a dynamical shell model. The proposed approach
has been tested on olivine NaFePO4, which is a promising cathode material for
Na-ion batteries. The calculated Na-ion diffusion and structural properties
have been compared with the available experimental data and with the results
obtained using MD and the original GSHMC method. Based on these tests, we claim
that the new technique is advantageous over MD and the conventional GSHMC and
can be recommended for studies of other solid-state electrode and electrolyte
materials whenever high accuracy and efficient sampling are critical for
obtaining tractable simulation results.
