Modeling surface motion effects in N2 dissociation on W(110): Ab initio molecular dynamics calculations and generalized Langevin oscillator model.

Francesco Nattino,Oihana Galparsoro,Francesca Costanzo,Geert-Jan Kroes,Maite Alducin,Ricardo Díez Muiño

doi:10.1063/1.4954773

Abstract

Accurately modeling surface temperature and surface motion effects is necessary to study molecule-surface reactions in which the energy dissipation to surface phonons can largely affect the observables of interest. We present here a critical comparison of two methods that allow to model such effects, namely, the ab initio molecular dynamics (AIMD) method and the generalized Langevin oscillator (GLO) model, using the dissociation of N2 on W(110) as a benchmark. AIMD is highly accurate as the surface atoms are explicitly part of the dynamics, but this advantage comes with a large computational cost. The GLO model is much more computationally convenient, but accounts for lattice motion effects in a very approximate way. Results show that, despite its simplicity, the GLO model is able to capture the physics of the system to a large extent, returning dissociation probabilities which are in better agreement with AIMD than static-surface results. Furthermore, the GLO model and the AIMD method predict very similar energy transfer to the lattice degrees of freedom in the non-reactive events, and similar dissociation dynamics.

Highlights

The dissociation of diatomic molecules on metal surfaces represents the simplest class of molecule-metal surface reactions
We have found that the generalized Langevin oscillator (GLO) model and the ab initio molecular dynamics (AIMD) method qualitatively agree in how surface motion and surface temperature effects affect the dissociation probability of N2 on W(110)
The first observable that we consider in the comparison of the GLO model to the AIMD method is the dissociation probability

Summary

Introduction

The dissociation of diatomic molecules on metal surfaces represents the simplest class of molecule-metal surface reactions. The simplicity, is only apparent, as theory still struggles to achieve quantitative agreement with experiment on dynamical observables such as the dissociation probability for various molecule-surface systems.. One of the approximations on which state-of-the-art calculations often rely and which is often blamed for such discrepancies is the ideal and static surface approximation, which assumes the metal atoms to remain fixed at their equilibrium position during the whole course of the dynamics. This approximation enormously simplifies the complexity of the problem, reducing the dimensionality of the moleculesurface interaction potential to the six molecular degrees of freedom.

Objectives

Methods

Results

Conclusion