Abstract
Ab initio molecular dynamics with electronic friction (AIMDEF) is a valuable methodology to study the interaction of atomic particles with metal surfaces. This method, in which the effect of low-energy electron-hole (e-h) pair excitations is treated within the local density friction approximation (LDFA) [Juaristi et al., Phys. Rev. Lett. 100, 116102 (2008)], can provide an accurate description of both e-h pair and phonon excitations. In practice, its applicability becomes a complicated task in those situations of substantial surface atoms displacements because the LDFA requires the knowledge at each integration step of the bare surface electron density. In this work, we propose three different methods of calculating on-the-fly the electron density of the distorted surface and we discuss their suitability under typical surface distortions. The investigated methods are used in AIMDEF simulations for three illustrative adsorption cases, namely, dissociated ${\mathrm{H}}_{2}$ on Pd(100), N on Ag(111), and ${\mathrm{N}}_{2}$ on Fe(110). Our AIMDEF calculations performed with the three approaches highlight the importance of going beyond the frozen surface density to accurately describe the energy released into e-h pair excitations in case of large surface atom displacements.
Highlights
Many are the theoretical studies confirming that the fundamental properties in most elementary gas-surface processes are satisfactorily described by the Born-Oppenheimer approximation [1,2]
Our Ab initio molecular dynamics with electronic friction (AIMDEF) calculations performed with the three approaches highlight the importance of going beyond the frozen surface density to accurately describe the energy released into e-h pair excitations in case of large surface atom displacements
We have shown that the differences in the densities are small, it is not clear that they will be manifested as small differences in the dynamical magnitudes for, at least, three reasons: (i) the surface atom displacements vary in magnitude and are in persistent change along the trajectory, resulting in configurations where the different models can provide a fluctuactingly faithful description of the bare surface density; (ii) the friction coefficient η is not linearly dependent on nsur; and (iii) since the friction force is proportional to the projectile velocity, the electron density alone gives incomplete information about the e-h pairs excitation
Summary
Many are the theoretical studies confirming that the fundamental properties in most elementary gas-surface processes are satisfactorily described by the Born-Oppenheimer approximation [1,2]. The challenge in present thermal and hyperthermal gas-surface simulations is to provide a reliable description of the two main energy exchange channels that may affect the dynamics and reactivity of gas-phase species on solid surfaces, namely, phonon excitations and electron-hole (e-h) pair excitations In the end, these are the mechanisms that dictate the thermalization rate and, the mean traveled length of the nascent adsorbates. The section ends by analyzing the performance of each density model under extreme reliable conditions of large surface atoms displacements as those occurring upon equilibration of the adsorbates on the adsorption wells.
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