(307e) Nonadiabatic Effects and Creation of Electronic Excitations during Dissociation on Metal Nanoparticles

Authors: 
Montemore, M. M., Harvard University
Kaxiras, E., Harvard University
The Born-Oppenheimer approximation, which assumes that the electrons are always in their ground state, is widely used in density functional theory (DFT) studies of catalytic processes. These calculations have been quite successful in explaining a large number of catalytic phenomena. However, electronic excitations are easily induced in metal surfaces, due to the lack of a band gap. Here, we show that processes on catalytic surfaces may induce electronic excitations, which are not captured by simulations using the Born-Oppenheimer approximation.

We performed non-adiabatic dynamics using real-time, time-dependent DFT, propagating the nuclei using Ehrenfest dynamics. We study several trajectories of an N2 molecule interacting with Ru13 and Ru147 nanoparticles. These simulations show that, during the adsorption and dissociation processes, a significant amount of energy can be dissipated into electronic degrees of freedom, comparable to the amount of energy dissociated into ionic vibrations. The excitations initially take the form of electron-hole pairs, but after tens of fs they relax into hot electrons. This suggests that the electronic structure of catalytic surfaces may, transiently, be quite different from the ground state.