Dresden 2020 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 52: Quantum Dynamics, Decoherence and Quantum Information

DY 52.12: Talk

Thursday, March 19, 2020, 18:00–18:15, HÜL 186

Spin-mapping approach for nonadiabatic molecular dynamics — •Johan E. Runeson and Jeremy O. Richardson — Laboratory of Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland

An open problem in computational physics and chemistry is to rigorously combine the quantum description of nonadiabatic processes with the simple classical trajectories of molecular dynamics (MD) simulations. Nonadiabatic processes are relevant for many modern applications, for example light harvesting in chromophores, and are characterized by the breakdown of the Born-Oppenheimer approximation.

In my talk I will show a simple way to achieve this for a general N-level quantum system in a classical environment, without invoking the surface-hopping ansatz. The key idea is to assign additional variables to each trajectory to describe the electronic states, in addition to the nuclear coordinates and momenta. These variables originate from a Wigner-like representation of the Bloch vector, that can be viewed as a classical spin. We have showed[1] how to derive a mixed quantum-classical method in this way, which shares the same equations of motion as in Ehrenfest dynamics, but differs in an important way in how initial distributions and observables are defined. This vastly improves results in benchmark systems of population dynamics compared to the conventional Ehrenfest method, without adding computational cost.

[1] J. E. Runeson and J. O. Richardson, J. Chem. Phys. 151, 044119 (2019)