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Gas-surface scattering involves the conversion of energy in different forms in the impinging molecule, possible bond breaking and forming, and the energy transfer across gas-solid interface. Possible energy dissipation channels include adiabatic energy transfer to the motion of surface phonons and non-adiabatic interactions with surface electron-hole pairs. A complete understanding of the interplay of energy dissipation and physical/chemical changes in the molecule is vital for many important applications such as materials fabrication and heterogenous catalysis. Gas-surface encounters may occur where non-adiabatic effects are negligible. Two such systems were investigated, both with ample experimental data. One is concerned with the scattering of small molecules, i.e., H2O, CO2 and glycine, from a highly ordered pyrolytic graphite (HOPG) surface. Molecular dynamics (MD) simulations revealed that each of the three molecules scattered from the surface via three mechanisms: impulsive scattering, extended impulsive scattering, and trapping. The results showed that the scattering dynamics are heavily dependent on the strength of molecule−surface interaction. Molecules with a stronger attraction tend to have longer residence times on the surface and consequently experience more translational energy dissipation and vibrational excitation. The other work investigated the interaction of the N atom with the HOPG surface, including the adsorption, diffusion of the N atom and the formation of N2 through different mechanisms. While N2 recombination does not have a barrier with Eley–Rideal (ER) pathway, the Langmuir–Hinshelwood (LH) pathway is limited by the diffusion barrier of the adsorbed N atom. The N2 molecule formed by recombinative desorption is found to be bother translationally and internally hot. These possible pathways and mechanisms are helpful for understanding the hyperthermal collision experiment of a

Great success has been achieved in the modeling of gas-surface elementary processes by the use of the Born-Oppenheimer approximation. However, in metal surfaces low energy electronic excitations are generated even by thermal and hyperthermal molecules due to the absence of band gaps in the electronic structure. This shows the importance of performing dynamical simulations that incorporate non-adiabatic effects to analyze in which way they affect most common gas-surface reactions. Here we review recent theoretical developments in this problem and their application to the study of the effect of electronic excitations in the adsorption and relaxation of atoms and molecules in metal surfaces, in scattering processes, and also in recombinative processes between impinging atoms and adsorbates at the surface. All these studies serve us to establish what properties of the gas-surface interaction favor the excitation of low-energy electron-hole pairs. A general observation is that the nature of these excitations usually requires long lasting interactions at the surface in order to observe deviations from the adiabatic behaviour. We also provide the basis of the local density friction approximation (LDFA) that have been used in all these studies, and show how it has been employed to perform ab initio molecular dynamics with electronic friction (AIMDEF). As a final remark, we will shortly review on recent applications of the LDFA to successfully simulate desorption processes induced by intense femtosecond laser pulses.

Former calculations showed that atomic N incident at energies of a few eV on N-covered Ag(1 1 1) forms N2 molecules by the Eley-Rideal (ER) mechanism, i.e. by direct pick-up of adsorbates. Here, we calculate the azimuthal angle distributions and the rovibrational energies of those ER products. We observe a non-trivial angle dependence that may result in very low in-plane ER yield for some given incident azimuthal angles. We find that most of the energy released upon NN bond formation, about 7 eV, is stored in the rovibrational degrees of freedom independently of the incidence energy considered.

In honoring the seminal contribution of Henry Eyring and Michael Polanyi who first introduced the concept of potential energy surfaces (PESs) to describe chemical reactions in gas-phase [Z. Phys. Chem. 12, 279-311, (1931)], this work comes to review and assess state-of-the-art approaches towards first-principle based modeling in the field of gas-surface dynamics. Within the Born- Oppenheimer and frozen surface approximations, the O2-Ag(100) interaction energetics are used as a showcase system to accentuate the complex landscape exhibited by the PESs employed to describe the impingement of diatomics on metal substrates and draw attention to the far-from-trivial task of continuously representing them within all six molecular degrees of freedom. To this end, the same set of ab initio reference data obtained within Density Functional Theory (DFT) are continuously represented by two different state-of-the-art high-dimensional approaches, namely the Corrugation-Reducing Procedure and Neural Networks. Exploiting the numerically undemanding nature of the resulting representations, a detailed static evaluation is performed on both PESs based on an extensive global minima search. The latter proved particularly illuminating in revealing representation deficiencies which affect the dynamical picture yet go otherwise unnoticed within the so-called >divide-and-conquer> approach.© by Oldenbourg Wissenschaftsverlag, München.