OberflächenHoppingMethoden

Oberflächenhopping, known in English as surface hopping, is a computational approach used to simulate nonadiabatic dynamics in molecular systems. It combines classical nuclear motion with stochastic transitions between electronic potential energy surfaces, allowing atoms to move on one surface at a time while occasional hops switch the electronic state.

In typical surface hopping simulations, nuclei are propagated using Newtonian dynamics on the current electronic surface. Nonadiabatic couplings between electronic states are evaluated to determine hop probabilities. The most common implementation uses the fewest switches criterion: hops are attempted in a way that minimizes the number of surface changes while reproducing the overall population transfer between states. If a hop is accepted, the system switches to the new electronic surface and nuclear velocities are adjusted, usually along the direction of the nonadiabatic coupling, to conserve total energy. If energy conservation cannot be achieved, the hop is rejected, a situation known as a frustrated hop.

Originating from work by John Tully in the 1990s, surface hopping has become a standard tool for modeling photoinduced processes where electronic and nuclear dynamics are strongly coupled. Variants and refinements include decoherence corrections to mitigate spurious coherence between surfaces and alternative hopping schemes that seek to improve accuracy for specific systems.

Applications of Oberflächenhopping span photochemistry, radiation biology, and materials science, where processes such as internal conversion, intersystem crossing, and charge transfer occur on ultrafast timescales. While powerful, the method remains approximate: it relies on semiclassical nuclei, relies on electronic structure calculations, and its results depend on the chosen surface set and coupling terms.