Efficient Path Integral Dynamics

Systems, where a fully atomistic treatment is not feasible, can be modelled as dissipative quantum systems coupled to their environment. Time-dependent properties and observables such as spectra can then be obtained from the evolution of the reduced density matrix. A versatile method for the time-dependent simulation of such systems is the QUasi-Adiabatic Path Integral (QUAPI) approach. We have developed a powerful parallel implementation of QUAPI, including methodological advances that allow to speed up simulations by several orders of magnitude. Figure_MACGIC-QUAPI_FMO_2This is achieved by Mask Assisted Coarse Graining of the Influence Coefficients (MACGIC-QUAPI) [J. Chem. Phys. 146, 214101 (2017)] and inclusion of low scaling sorting and merging algorithms in on-the-fly path selection.

The MACGIC-QUAPI method successfully interpolates between the weak- and strong-coupling regimes of excitation energy and electron transfer. It can be applied to large systems, demonstrated for a fully coupled 24-state model of the Fenna-Mathews-Olsen complex. Convergence to numerical exact result was confirmed by comparison to high-level hierarchical equations of motion simulations. Furthermore, the algorithmic structure allows for efficient parallelization on modern high-performance computing hardware.