Interplay between electronic and phononic energy dissipation channels in the adsorption of CO on Cu(110)

TL;DR

This study quantifies the relative contributions of phonon and electron-hole pair dissipation in CO adsorption on Cu(110) by comparing phonon-only and phonon+electronic-friction models using quasi-classical trajectories on a full-dimensional ANN-PES trained from vdW-DF2 DFT data. The results show that phonon-mediated energy transfer dominates the initial adsorption step, with electronic friction mainly speeding up the long-time accommodation without altering the sticking probability $S_0$ or the preferred adsorption geometry. Final adsorbed molecules remain at top sites with $Z_{CM}$ around 2.65 Å and orientation near $\theta=0^\circ$, while electronic friction slightly refines the final energy distribution and narrows $Z_{CM}$, without affecting lateral diffusion significantly. Overall, for CO/Cu(110) with a moderate chemisorption well, phonon-only models accurately predict $S_0$, whereas nonadiabatic channels are needed to capture the complete energy-relaxation dynamics on longer timescales.

Abstract

In this work, we investigate the relative importance of electronic and phononic energy dissipation during the molecular adsorption of CO on Cu(110). Initial sticking probabilities as a function of impact energy for CO impinging at normal incidence at a surface temperature of 90 K were computed using classical trajectory simulations. To this aim, we use a full-dimensional potential energy surface constructed using an atomistic neural network trained on density functional theory data obtained with the nonlocal vdW-DF2 exchange-correlation functional. Two models are compared: one allowing only energy transfer and dissipation from the molecule to lattice vibrations, and the other also incorporating the effect of molecular energy loss due to the excitation of electron-hole pairs, modeled within the local-density friction approximation. Our results reveal, firstly, that the molecule mainly transfers energy to lattice vibrations, and this channel determines the adsorption probabilities, with electronic friction playing a minor role. Secondly, once the molecule is trapped near the surface (where electronic density is higher), electron-hole pair excitations accelerate energy dissipation, significantly promoting CO thermalization. Still, the faster energy dissipation when electron-hole pair excitations are accounted for accelerates the accommodation of the adsorbed molecules in the chemisorption well but does not significantly alter their lateral displacements over the surface.

Figures (8)

• Figure 1: S$_{0}$ values as a function of the initial CM translational kinetic energy of the molecule, E$_{\mathrm{i}}$. Black (red) solid line, Ph+EF (Ph) for (6$\times$5) supercell; black dot-dashed line, Ph+EF for (3$\times$2) supercell; green dashed line, BOSS model for (6$\times$5) supercell. The blue diamonds represent experimental data for CO/Cu(110) at T$_{\mathrm{S}}$=90 K Kunat2001, and violet squares correspond to experiments for CO/Cu(111) at T$_{\mathrm{S}}$=85 K Kneitz1999aKneitz1999b.
• Figure 2: Fraction of molecules that remain close to the surface, F$_\text{close}$, as a function of maximum integration time for Ph simulations at different incidence energies: 0.046, 0.575, 1.2, and 2 eV. Asymptotic S$_0$ values are represented by dashed lines.
• Figure 3: Average total kinetic energy of adsorbed CO molecules, $\left\langle E_{kin} \right\rangle$ as a function of time, for different impact energies: (a) 0.046 eV, (b) 0.575 eV, (c) 1.2 eV, and (d) 2.0 eV. Insets show the average molecular CM, $\left\langle Z_{CM}\right\rangle$ as a function of time for Ph simulations (Ph+EF results are similar and have been omitted for clarity). Red: including energy exchange with phonons, black: including phonons and electronic friction.
• Figure 4: Time evolution of the mean temperature of mobile Cu atoms, $\left\langle T_{\text{Cu}} \right\rangle$, for adsorbed CO molecules: (a) E$_{\mathrm{i}}$=0.046 eV, (b) E$_{\mathrm{i}}$=2 eV. Red and black curves correspond to Ph and Ph+EF simulations, respectively.
• Figure 5: Upper panels: $\left\langle E_{kin,CM}\right\rangle$ values at different incidence energies: (a) 0.046 eV, (b) 2.0 eV. Lower panels: $\left\langle E_{kin,int}\right\rangle$ values at different incidence energies: (c) 0.046 eV, (d) 2.0 eV (d). Red and black curves correspond to Ph and Ph+EF simulations, respectively.