Methods for accurately computing the interaction of molecules with metal surfaces are critical to understanding and thereby improving heterogeneous catalysis. We introduce an implementation of the specific reaction parameter (SRP) approach to density functional theory (DFT) that carries the method forward from a semiquantitative to a quantitative description of the molecule-surface interaction. Dynamics calculations on reactive scattering of hydrogen from the copper (111) surface using an SRP-DFT potential energy surface reproduce data on the dissociative adsorption probability as a function of incidence energy and reactant state and data on rotationally inelastic scattering with chemical accuracy (within approximately 4.2 kilojoules per mole).

Ni-CeO2 is a highly efficient, stable and non-expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO2 at temperatures as low as 300 K, generating CHx and COx species on the surface of the catalyst. Strong metal-support interactions activate Ni for the dissociation of methane. The results of density-functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO2-x (111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CHx or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.

We quantitatively evaluate the contribution of electron-hole pair excitations to the reactive dynamics of H 2 on Cu(110) and N 2 on W(110), including the six dimensionality of the process in the entire calculation. The interaction energy between molecule and surface is represented by an ab initio six-dimensional potential energy surface. Electron friction coefficients are calculated with density functional theory in a local density approximation. Contrary to previous claims, only minor differences between the adiabatic and nonadiabatic results for dissociative adsorption are found. Our calculations demonstrate the validity of the adiabatic approximation to analyze adsorption dynamics in these two representative systems. DOI: 10.1103/PhysRevLett.100.116102 PACS numbers: 82.65.+r, 34.35.+a, 68.49.Df, 82.20.Kh The adiabatic Born-Oppenheimer approximation is ubiquitous in the theoretical study of elementary reactive processes at surfaces. Still, there is ample experimental evidence of electronic excitations associated to gas or surface reactions, that can potentially break down the applicability of the adiabatic approach. Electron-hole pairs appear, for instance, in the detection of chemicurrents during the chemisorption of gas-phase species on thin metal films [1,2], as well as in the measurement of electron emission following the scattering of molecules in highlyexcited vibrational states on metal surfaces [3,4]. Although the existence of energy dissipation through electron-hole (e-h) pair excitations is widely accepted, there is not a definite quantitative answer on the role of electronic excitations in the adsorption and reaction rates of diatomic molecules at metal surfaces [5].Laursen et al. [6] predicted that e-h pair excitations should alter substantially the adsorption dynamics of H 2 in Cu (110). Contravening this prediction, full sixdimensional (6D) adiabatic calculations of the dynamics based on an ab initio potential energy surface have been shown to provide a good description of the experimental results on this system [7]. Measurements of the dissociative adsorption and diffractive scattering of H 2 on Pt(111) are reasonably well described within the adiabatic approximation as well [8]. For heavier molecules, it was claimed that strong energy dissipation effects due to the excitation of e-h pairs are responsible for the strong disagreement between (adiabatic) theoretical and experimental sticking coefficients for N 2 on Ru(0001) [9,10]. Díaz et al. [11] showed afterwards that when the full dimensionality of the process is taken into account, adiabatic calculations are much closer to experiments. This result suggests that nonadiabatic effects might be smaller than previously predicted. Still, the lack of a theoretical calculation, based on state-of-the-art interaction potentials, that explicitly includes the e-h pair excitation channel and the full dimensionality of the process keeps this controversy open.In this Letter, we evaluate the contribution of e-h pair excitations to the dissociative adsorp...

An efficient method is proposed to construct the six-dimensional Potential Energy Surface (PES) for diatomic molecule-surface interactions from low dimensional cuts obtained in ab initio calculations. The efficiency of our method results from a corrugation-reducing procedure based on the observation that most of the corrugation in a molecule-surface PES is already embedded in the atom-surface interactions. Hence, substraction of the latter leads to a much smoother function which makes accurate interpolations possible. The proposed method is a general one and can be implemented in a systematic way for any system. Its efficiency is illustrated for the case of H2/Pd(111) by using recent ab initio data. We report also the results of very stringent checks against ab initio calculations not used in the interpolation. These checks show the high accuracy of our method.

H(2) scattering and dissociative adsorption on the W(100)-c(2 × 2)Cu surface alloy is studied based on DFT calculations. A strongly site dependent reactivity is observed in line with results obtained for the density of states projected onto the W and Cu atoms of the topmost layer. H(2) dissociation on a defect free terrace of W(100)-c(2 × 2)Cu is found to be a non-activated process like on W(100), despite the reduction of the number of energetically accessible dissociation pathways at low impact energies due to the presence of Cu atoms. A prominence of dynamic trapping and a reduction of the efficacy of trapping to promote dissociation is also verified, leading to a decrease of the initial sticking probability as a function of the molecular impact energy, in qualitative agreement with experimental findings. The heterogeneous reactivity is also evidenced by two different kinds of reflection events at low energies. Its combination gives rise to a broad specular peak superimposed on a cosine-like angular distribution of scattered molecules which is in good agreement with available experimental data.

We present new experimental and theoretical results for reactive scattering of dihydrogen from Cu(100). In the new experiments, the associative desorption of H 2 is studied in a velocity resolved and final rovibrational state selected manner, using time-of-flight techniques in combination with resonance-enhanced multi-photon ionization laser detection. Average desorption energies and rotational quadrupole alignment parameters were obtained in this way for a number of (v = 0, 1) rotational states, v being the vibrational quantum number. Results of quantum dynamics calculations based on a potential energy surface computed with a specific reaction parameter (SRP) density functional, which was derived earlier for dihydrogen interacting with Cu (111), are compared with the results of the new experiments and with the results of previous molecular beam experiments on sticking of H 2 and on rovibrationally elastic and inelastic scattering of H 2 and D 2 from Cu(100). The calculations use the Born-Oppenheimer and static surface approximations. With the functional derived semi-empirically for dihydrogen + Cu(111), a chemically accurate description is obtained of the molecular beam experiments on sticking of H 2 on Cu(100), and a highly accurate description is obtained of rovibrationally elastic and inelastic scattering of D 2 from Cu(100) and of the orientational dependence of the reaction of (v = 1, j = 2 − 4) H 2 on Cu(100). This suggests that a SRP density functional derived for H 2 interacting with a specific low index face of a metal will yield accurate results for H 2 reactively scattering from another low index face of the same metal, and that it may also yield accurate results for H 2 interacting with a defected (e.g., stepped) surface of that same metal, in a system of catalytic interest. However, the description that was obtained of the average desorption energies, of rovibrationally elastic and inelastic scattering of H 2 from Cu(100), and of the orientational dependence of reaction of (v = 0, j = 3 − 5, 8) H 2 on Cu(100) compares less well with the available experiments. More research is needed to establish whether more accurate SRP-density functional theory dynamics results can be obtained for these observables if surface atom motion is added to the dynamical model. The experimentally and theoretically found dependence of the rotational quadrupole alignment parameter on the rotational quantum number provides evidence for rotational enhancement of reaction at low translational energies.

We study the dynamics of transient hot H atoms on Pd(100) that originated from dissociative adsorption of H 2 . The methodology developed here, denoted AIMDEF, consists of ab initio molecular dynamics simulations that include a friction force to account for the energy transfer to the electronic system. We find that the excitation of electron-hole pairs is the main channel for energy dissipation, which happens at a rate that is five times faster than energy transfer into Pd lattice motion. Our results show that electronic excitations may constitute the dominant dissipation channel in the relaxation of hot atoms on surfaces. DOI: 10.1103/PhysRevLett.112.103203 PACS numbers: 68.43.-h, 34.35.+a, 34.50.Bw, 82.20.Gk Electron-hole (e-h) pair excitations are an unquestioned efficient energy drain in the interaction of fast atoms with solids and surfaces [1][2][3][4]. In contrast, the relevance of this dissipation channel in gas-surface interactions that involve energies up to a few eV is not so clear. It depends not only on the specific system, but also on the elementary process considered, as shown by different studies on scattering [5][6][7][8][9][10][11][12] and adsorption [6,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] of atoms and molecules on surfaces. Low-energy e-h pair excitations have been detected as chemicurrents on Schottky diode devices during the chemisorption of atomic and molecular species on metals [13][14][15]. The correlation found between chemicurrent intensities and adsorption energies is a strong indication that a large fraction of the energy dissipated in both the dissociative and nondissociative adsorption processes is used to excite e-h pairs. However, this strongly contrasts with examples showing that the dissociative adsorption is reasonably well described within the electronically adiabatic approach, which neglects the coupling between electronic excitations and the nuclear motion [6,[18][19][20]23,25], and that the effect of electronic energy dissipation seems negligible [21,24,26]. Therefore, a question that is raised here is at what stage of the dissociative adsorption process e-h pair excitations do become relevant.In a typical adsorption event, the incoming gas species gain additional kinetic energy when entering the attractive adsorption well. In the particular case of dissociative adsorption, this energy gain can lead to the formation of so-called "hot" atoms or fragments, with energies much larger than the corresponding thermal energies of the substrate atoms. The formed hot species will then propagate along the surface until they dissipate the excess kinetic energy and finally accommodate at a stable adsorption position. This stage of the dissociative adsorption process, where the relevance of e-h pair excitations has been traditionally neglected, is the focus of the present work.In this Letter we show that while e-h pair excitation may not be relevant on the molecule-bond-breaking time scale, it is an efficient dissipative channel in the subsequent relaxation of the...

Juaristi et al. Reply: In the preceding Comment [1] on our recent Letter [2], Luntz et al. claim that their results show that the local density approximation for electronic friction (LDAF) is in general not reliable for estimating the electronic friction for molecules on metal surfaces. This is an unfounded statement based on very limited information.Our LDAF calculation for the friction coefficient involves at most two further approximations as compared to those involved in the model used by Luntz et al.. (i) First, a local approximation for the electronic density is used. This is acknowledged to be a reasonable approximation. The LDAF was shown to be appropriate for calculations of the friction coefficient for atoms in metal surfaces, incidentally by some of the authors of the comment [3]. (ii) An additional approximation is that two-center effects are disregarded. Two-center effects were shown not to change the order of magnitude in the case of H 2 [4], but no studies in other systems have been performed to our knowledge.