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The classical trajectory method in a quantum spirit assigns statistical weights to classical paths on the basis of two semiclassical corrections: Gaussian binning and the adiabaticity correction. This approach was recently applied to the heterogeneous gas–surface reaction between H2 in its internal ground state and Pd(111) surface e.g. [A. Rodríguez-Fernández et al., J. Phys. Chem. Lett., 2019, 10, 7629]. Its predictions of the sticking and state-resolved reflection probabilities were found to be in surprisingly good agreement with those of exact quantum time-dependent calculations where standard quasi-classical trajectory calculations failed. We show in this work that the quality of the previous calculations is maintained or even improved when H2 is rotationally excited.

When elementary reactive processes occur at such low energies that only a few states of reactants and/or products are available, quantum effects strongly manifest and the standard description of the dynamics within the classical framework fails. We show here, for H scattering on Pd(111), that by pseudoquantizing in the spirit of Bohr the relevant final actions of the system, along with adequately treating the diffraction-mediated trapping of the incoming wave, classical simulations achieve an unprecedented agreement with state-of-the-art quantum dynamics calculations.

Adsorption dynamics of N2 on the W(100) surface is studied by means of quasi-classical trajectories making use of a six-dimensional potential energy surface obtained from density functional theory calculations. In our simulations, van der Waals (vdW) interactions are accounted for by using the vdW-DF2 functional. In view of the comparison with experiments, we show that this leads to a good description of the adsorption dynamics, providing a significant improvement with respect to semi-local exchange-correlation functionals used in the past. Particular emphasis is placed on the description of nonactivated pathways, leading to either dissociation or molecular adsorption. Dynamics calculations are performed within the generalized Langevin oscillator (GLO) model in order to simulate the energy exchange between molecule and surface atoms. Electron-hole (e-h) pair excitations are also implemented in the dynamics via the local density friction approximation (LDFA). Overall adsorption probability, including dissociative and nondissociative mechanisms, is enhanced when molecules can lose energy through surface phonons and electronic excitations. However, the energy exchange with phonons has a larger influence in the adsorption probability than e-h pair excitations. Nondissociative molecular adsorption only takes place when such energy dissipation channels are included in the simulations, underlying the importance of GLO and LDFA models in such theoretical studies.

The reactive dynamics of N on W(100) has been investigated by means of quasi-classical trajectory calculations using an interpolated six-dimensional potential energy surface (PES) based on density functional theory energies obtained employing the vdW-DF2 functional. The dynamics are compared to those obtained using the PW91 functional and to experimental data. The results show that the new PES provides a significant improvement in the description of the reactivity in this system. We show that the long standing problem that constituted the large qualitative disagreement between the simulations performed with the PW91-PES and the experiments was due to the presence of energy barriers in the entrance channel that disappear when vdW forces are accounted for.

The inelastic scattering dynamics of N2 off W(001) has recently been the subject of theoretical investigations, which were found to be unable to describe low-collision-energy molecular beam experiments. This discrepancy was suggested to originate from the neglect of van der Waals interactions in the construction of the potential energy surface. By making use of a newly developed potential energy surface, accounting for such dispersion interactions, we show that quasi-classical dynamics simulations, including dissipation to surface electrons and phonons, lead to an adequate description of the low-collision-energy experiments and, more specifically, the trapping-desorption component of inelastic scattering. This work highlights the prominent influence of van der Waals forces on gas–surface dynamics observables in the low-collision-energy regime.

Using adiabatic and nonadiabatic quasiclassical molecular dynamics simulations within the single adsorbate limit, we study the dependence on the incidence angle of the Eley-Rideal (ER) recombination of H and N on the (100) and (110) tungsten surfaces. In the nonadiabatic simulations, effects due to electron-hole pair excitations and the energy exchange between the recombination partners and the surface lattice are included in the dynamics by combining the local density friction approximation and the generalized Langevin oscillator model. Our adiabatic and nonadiabatic results, which are qualitatively similar, show that the incidence angle affects much more N recombination than H recombination due mainly to the higher corrugation of the potential energy surface for the former case. In particular, for N abstraction from W(110), we find a very efficient ER recombination pathway at grazing incidence angles. This new mechanism significantly influences the energy partition among the different degrees of freedom of the outgoing molecules. We also find that the energy losses only depend slightly on the incidence geometry and that, as in normal incidence, they are dominated by phonons in the case of N recombination and by electron-hole pair excitations in the case of H recombination.

Adiabatic and non-adiabatic quasiclassical molecular dynamics simulations are performed to investigate the role of the crystal face on hot-atom abstraction of H adsorbates by H scattering from covered W(100) and W(110). On both cases, hyperthermal diffusion is strongly affected by the energy dissipated into electron-hole pair excitations. As a result, the hot-atom abstraction is highly reduced in favor of adsorption at low incidence energy and low coverages, i.e., when the mean free path of the hyperthermal H is typically larger. Qualitatively, this reduction is rather similar on both surfaces, despite at such initial conditions, the abstraction process involves more subsurface penetration on W(100) than on W(110).

Using molecular dynamics simulations, we predict that the inclusion of nonadiabatic electronic excitations influences the dynamics of preadsorbed hydrogen abstraction from the W(110) surface by hydrogen scattering. The hot-atom recombination, which involves hyperthermal diffusion of the impinging atom on the surface, is significantly affected by the dissipation of energy mediated by electron–hole pair excitations at low coverage and low incidence energy. This issue is of importance as this abstraction mechanism is thought to largely contribute to molecular hydrogen formation from metal surfaces.

Quasiclassical molecular dynamics simulations are performed to investigate energy dissipation to the (100) and (110) tungsten surfaces upon Eley–Rideal (ER) recombination of H2 and N2. Calculations are carried out within the single adsorbate limit under normal incidence. A generalized Langevin surface oscillator (GLO) scheme is used to simulate the coupling to phonons, whereas electron–hole (e-h) pair excitations are implemented using the local density friction approximation (LDFA). Phonon excitations are found to reduce the ER reactivity for N2 recombination, but do not affect H abstraction. In contrast, the effect of e-h pair excitations on the ER recombination cross section is small for N2, but can be important for H2. The analysis of the energy lost by the recombined species shows that most of the energy is dissipated into phonon excitations in the N2 recombination and into electronic excitations in the H2 recombination. In all cases, the energy dissipated into e-h pairs is taken away from the translational kinetic energy of the formed molecules, whereas dissipation to phonons, only significant for N2, also affects vibration. Interestingly, the electron mediated energy losses are found to be smaller in the case of N2 when surface motion is allowed.

The scattering of atomic nitrogen over a N-pre-adsorbed W(100) surface is theoretically described in the case of normal incidence off a single adsorbate. Dynamical reaction mechanisms, in particular Eley-Rideal (ER) abstraction, are scrutinized in the 0.1-3.0 eV collision energy range and the influence of temperature on reactivity is considered between 300 and 1500 K. Dynamics simulations suggest that, though non-activated reaction pathways exist, the abstraction process exhibits a significant collision energy threshold (0.5 eV). Such a feature, which has not been reported so far in the literature, is the consequence of a repulsive interaction between the impinging and the pre-adsorbed nitrogens along with a strong attraction towards the tungsten atoms. Above threshold, the cross section for ER reaction is found one order of magnitude lower than the one for hot-atoms formation. The abstraction process involves the collision of the impinging atom with the surface prior to reaction but temperature effects, when modeled via a generalized Langevin oscillator model, do not affect significantly reactivity. © 2012 American Institute of Physics.