Nonadiabatic events are involved in important biological processes such as energy, electron, and proton transfers. Due to the complexity of biological systems, mixed quantum-classical approaches are widely adopted where the system of interest is described with quantum mechanics and its remainder is treated with relatively simple classical mechanics. However, approximate methods cannot fully separate the dynamics on multiple energy surfaces and thus cannot exactly explain decoherence. This decoherence problem causes unphysical behaviors such as oscillatory branching ratios and incorrect long-time populations. Here, we present our investigation on this issue with a variant of Poisson bracket mapping equation (PBME) that can be reasonably employed to long-time simulations of large systems. It is found that this method consistently outperforms Ehrenfest or mean-field approach. However, for cases with extended regions of state coupling, depending on the initial momentum, PBME and its variant do not recover correct equilibrium populations. With these, we discuss the future directions for improving the PBME-style mixed quantum-classical approaches.

Decoherence in nonadiabatic dynamics from an approximate mixed quantum-classical Poisson bracket mapping equation formalism

249th National Meeting (2015)

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