Six-Dimensional Quantum Dynamics of Dissociative Chemisorption of (v=0,j=0)

Geert–Jan Kroes

¹

,

Evert Jan Baerends

²

,

R. C. Mowrey

³

Abstract

Six-dimensional quantum dynamics calculations are now possible for fully activated dissociative chemisorption of H 2 . We present results for the reaction of (y 0, j 0) H 2 on Cu(100). The potential energy surface was taken from density functional theory (DFT), using the generalized gradient approximation. Comparison to experiment suggests that, on average, the DFT method overestimates the barriers to dissociation by 0.18 eV for H 2 1 Cu͑100͒. [S0031-9007(97) PACS numbers: 82.65. Jv, 34.50.Dy, 34.50.Ez, 82.20.Kh The reaction of H 2 on copper is the most studied example of translationally activated molecular dissociation on a metal surface. For the reaction on the (100) face, direct information is available from molecular beam experiments [1]. Indirect information comes from experiments on associative desorption, invoking the principle of detailed balance [2]. The results [1,2] have been used in a fit [3] which describes the reaction probability R y ͑E i ͒ as an S-shaped function of the normal incidence energy E i ,Here, A is the saturation value of the reaction probability. The dynamical threshold E 0 is a measure of the average barrier height, being the energy E i at which R y 0.5 3 A, and W is the width of the curve. The use of the quantum number y as a label signifies a dependence on the initial vibrational state y of H 2 (y is 0 or 1). While dynamics calculations have explained several experimental trends in the activated dissociation of H 2 on copper, they have so far failed in accurately reproducing the experimental reaction probabilities. Assuming that the Born-Oppenheimer approximation can be used (i.e., neglecting electron-hole pair excitations [4]) and that surface phonons can be neglected [5], accurate calculations can be done if two criteria are met. First, an accurate potential energy surface (PES), describing the electronic molecule-surface interaction as a function of all molecular degrees of freedom, should be available. Second, multidimensional quantum simulations of the reaction [6][7][8][9] suggest and classical calculations [10] show that the subsequent dynamics calculation should explicitly treat all six molecular degrees of freedom, if possible, on a quantum footing.An electronic structure approach with a claim to accuracy is now available. The method uses the generalized gradient approximation (GGA) [11,12] A good way of validating the new electronic structure method is to use a computed PES in 6D quantum dynamics computations to obtain reaction probability curves for comparison to experiment. However, so far 6D quantum calculations have been performed only for one unactivated dissociation problem ͓H 2 1 Pd͑100͔͒ [19]. For H 2 on copper, results are needed for higher collision energies, requiring the use of larger basis sets. So far no more than four degrees of freedom were treated with no approximations in quantum dynamical simulations of the reaction of H 2 on copper [6-9], though 6D calculations have been done in a mixed quantum-classical framework [20].We present results of a 6D q...

Reactive and diffractive scattering of H2 from Pt(111) studied using a six-dimensional wave packet method

“…Previous 6D calculations on H 2 ϩCu(100) likewise showed that inclusion of the rotational degrees of freedom leads to a decrease of the reaction probability. 51 For copper, the effect is larger due to barrier being later, leading to a stronger dependence of the potential barrier on the polar angle for Cu͑100͒. The important effect of the rotation involving on the magnitude of the reaction probability was first pointed out in reduced dimensionality quantum dynamics calculations of Nielsen et al 52 The lowest barrier to dissociation, 0.06 eV, is for the parallel orientation above the top site, with dissociation towards the bridge site.…”

Toward Detection of Electron-Hole Pair Excitation in H-atom Collisions with Au(111): Adiabatic Molecular Dynamics with a Semi-Empirical Full-Dimensional Potential Energy Surface

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Six-dimensional quasiclassical and quantum dynamics of H2 dissociation on the c(2 × 2)-Ti/Al(100) surface

“…Theoretical progress in gas-surface reaction dynamics 11,[25][26][27][28][29][30][31] Based on a slab model of one ML Ti covered Ti/Al(100) surface, 2 a 6D PES has been built by the density functional theory (DFT) (Refs. 43 and 44).…”