Dissociation and recombination of D2 on Cu(111): Ab initio molecular dynamics calculations and improved analysis of desorption experiments

Abstract

Obtaining quantitative agreement between theory and experiment for dissociative adsorption of hydrogen on and associative desorption of hydrogen from Cu(111) remains challenging. Particularly troubling is the fact that theory gives values for the high energy limit to the dissociative adsorption probability that is as much as two times larger than experiment. In the present work we approach this discrepancy in three ways. First, we carry out a new analysis of the raw experimental data for D2 associatively desorbing from Cu(111). We also perform new ab initio molecular dynamics (AIMD) calculations that include effects of surface atom motion. Finally, we simulate time-of-flight (TOF) spectra from the theoretical reaction probability curves and we directly compare them to the raw experimental data. The results show that the use of more flexible functional forms for fitting the raw TOF spectra gives fits that are in slightly better agreement with the raw data and in considerably better agreement with theory, even though the theoretical reaction probabilities still achieve higher values at high energies. The mean absolute error (MAE) for the energy E0 at which the reaction probability equals half the experimental saturation value is now lower than 1 kcal/mol, the limit that defines chemical accuracy, while a MAE of 1.5 kcal/mol was previously obtained. The new AIMD results are only slightly different from the previous static surface results and in slightly better agreement with experiment.

Performance of a Non-Local van der Waals Density Functional on the Dissociation of H2 on Metal Surfaces

“…Finally, note that the experimental value for D 2 /Cu(111) was originally reported to be χ v 0.54, 67 but this was based on a different definition of the vibrational efficacy, in which different values for P r,0 are used for v = 0 and 1. In figure 6 the reaction probability for (v = 0, J = 0, 2, 4, 6, 8) D 2 dissociating on Cu(111)is shown for both tested functionals, also comparing to the reaction probability curves extracted from experiments 81. The analysis of the experimental results showed that reaction first decreases with J, up to about J = 4, and then increases with J 67,81.…”

Methane dissociation on Pt(111): Searching for a specific reaction parameter density functional

“…On the one hand, the AIMD method has already been found [62,96] to underestimate the experimental surface temperature dependence of the dissociation probability of D 2 on Cu(111) [97]. On the other hand, the extent to which surface temperature enhances reactivity has been experimentally observed to decrease with increasing collision energy [9,50,51], and Schoofs et al [92] even reported that no dependence of the sticking probability on T s was observed (within their experimental sensitivity [98]) at E i ≈ 0.7 eV (about 0.3 eV lower than the collision energy that we have simulated).…”

Quantum State–Resolved Studies of Chemisorption Reactions

“…These full-dimensional calculations were used to test some of the approximations made in reduced-dimensionality calculations (139). They have been used to model H 2 on copper (22,140) and CHD 3 on Pt(111) (141-143) and on Ni(111) (139,144), but extension to CH 4 is difficult due to artificial IVR that can occur between bonds of the same frequency in classical calculations.…”

“…Rather than using a quantum approach to propagate the dynamics, Kroes and coworkers (22,(139)(140)(141)(142)(143)(144) use quasi-classical trajectory calculations in their ab initio molecular dynamics (AIMD) simulations of gas-surface reactions. One advantage of the AIMD treatment is that it includes all molecular degrees of freedom as well as the surface-atom motion, which is not yet possible using quantum dynamics.…”

“…The applicability of the BOA to gas-surface interactions is the subject of several recent reviews (17)(18)(19). Further approximations are often made in theoretical modeling of gas-surface reactions, including the use of density functional theory (DFT) (20) to describe electronic motion, as well as reduced-dimensional models (21) for treating nuclear motion either classically (22) or quantum mechanically (23).…”