Nonadiabatic Forward Flux Sampling for Excited-State Rare Events

Abstract

We present a rare event sampling scheme applicable to coupled electronic excited states. In particular, we extend the forward flux sampling (FFS) method for rare event sampling to a nonadiabatic version (NAFFS) that uses the trajectory surface hopping (TSH) method for nonadiabatic dynamics. NAFFS is applied to two dynamically relevant excited-state models that feature an avoided crossing and a conical intersection with tunable parameters. We investigate how nonadiabatic couplings, temperature, and reaction barriers affect transition rate constants in regimes that cannot be otherwise obtained with plain, traditional TSH. The comparison with reference brute-force TSH simulations for limiting cases of rareness shows that NAFFS can be several orders of magnitude cheaper than conventional TSH and thus represents a conceptually novel tool to extend excited-state dynamics to time scales that are able to capture rare nonadiabatic events.

LVC/MM: A Hybrid Linear Vibronic Coupling/Molecular Mechanics Model with Distributed Multipole-Based Electrostatic Embedding for Highly Efficient Surface Hopping Dynamics in Solution

“…All trajectories used a 2 fs time step (500,000 steps). The TIP3P water molecules and the two C–H bonds of thioformaldehyde were constrained to their equilibrium values using the RATTLE algorithm implemented in SHARC 3.0. , The temperature was set to 293 K via the Langevin thermostat implemented in SHARC …”

“…69,70 The temperature was set to 293 K via the Langevin thermostat 71 implemented in SHARC. 72 SHARC 29,60 is not able to perform simulations with periodic boundary conditions. Therefore, we utilized the droplet potential of Sankararamakrishnan et al 73 to keep the water droplet spherical, with a radius of about 19.8 Å.…”

Use of QM/MM Surface Hopping Simulations to Understand Thermally Activated Rare-Event Nonadiabatic Transitions in the Condensed Phase

“…Note that an alternative to the HST approach based on a combination of FSSH and forward sampling was recently published by Gonzalez, Dellago, and co-workers. 42 2.3. Velocity Reversal and Overestimation of Rates.…”

“…In practice, we have previously found strong numerical results from this modified HST method (where we also benchmarked the sensitivity of the method to the choice of dividing surface). Note that an alternative to the HST approach based on a combination of FSSH and forward sampling was recently published by Gonzalez, Dellago, and co-workers …”

Recovering Marcus Theory Rates and Beyond without the Need for Decoherence Corrections: The Mapping Approach to Surface Hopping

“…Unfortunately, the FSSH dynamics do not obey time-translation symmetry, and hence, the flux-correlation formalism does not rigorously give the same result as calculating the rate from direct population dynamics. A number of approaches for overcoming this issue have been suggested, such as using initial wave function amplitudes in the flux-correlation function generated from approximate backward-propagation schemes, , as well as the use of dynamically enhanced sampling in the form of forward-flux sampling . Here, to avoid making further approximations, we simply calculated the FSSH rate from direct population dynamics, which can be achieved due to the low computational cost of the model employed.…”