Scalable Ehrenfest Molecular Dynamics Exploiting the Locality of Density-Functional Tight-Binding Hamiltonian

To explore the science behind excited-state
dynamics in high-complexity
chemical systems, a scalable nonadiabatic molecular dynamics (MD)
technique is indispensable. In this study, by treating the electronic
degrees of freedom at the density-functional tight-binding level,
we developed and implemented a reduced scaling and multinode-parallelizable
Ehrenfest MD method. To achieve this goal, we introduced a concept
called patchwork approximation (PA), where the effective Hamiltonian
for real-time propagation of the electronic density matrix is partitioned
into a set of local parts. Numerical results for giant icosahedral
fullerenes, which comprise up to 6000 atoms, suggest that the scaling
of the present PA-based method is less than quadratic, which yields
a significant advantage over the conventional cubic scaling method
in terms of computational time. The acceleration by the parallelization
on multiple nodes was also assessed. Furthermore, the electronic and
structural dynamics resulting from the perturbation by the external
electric field were accurately reproduced with the PA, even when the
electronic excitation was spatially delocalized.