An Explicit and Symplectic Integrator for Quantum-Classical Molecular Dynamics

Relative error in QCMD energy for symplectic vs. non-symplectic integrator

Peter Nettesheim, Folkmar A. Bornemann, Burkhard Schmidt, and Christof Schütte

An explicit and symplectic integrator called PICKABACK for quantum-classical molecular dynamics is presented. The integration scheme is time reversible and unitary in the quantum part. We use the Lie formalism in order to construct a formal evolution operator which is split by the Strang splitting yielding the symplectic discretization PICKABACK. Finally the new method is compared with a widely used hybrid method in two examples: a collinear collision of a particle with a quantum oscillator and, additionally, a photodissociation process of an ArHCl molecule. It is shown that the PICKABACK algorithm is more stable and accurate at no additional numerical effort.

Chem. Phys. Lett. 256 (6), 581-588 (1996)