Effect of Surface Motion on the Rotational Quadrupole Alignment Parameter ofD2Reacting on Cu(111)

Abstract

Ab initio molecular dynamics (AIMD) calculations using the specific reaction parameter approach to density functional theory are presented for the reaction of D 2 on Cu(111) at high surface temperature (T s ¼ 925 K). The focus is on the dependence of reaction on the alignment of the molecule's angular momentum relative to the surface. For the two rovibrational states for which measured energy resolved rotational quadrupole alignment parameters are available, and for the energies for which statistically accurate rotational quadrupole alignment parameters could be computed, statistically significant results of our AIMD calculations are that, on average, (i) including the effect of the experimental surface temperature (925 K) in the AIMD simulations leads to decreased rotational quadrupole alignment parameters, and (ii) including this effect leads to increased agreement with experiment. DOI: 10.1103/PhysRevLett.108.236104 PACS numbers: 68.43.Bc, 34.35.+a, 82.65.+r Experiments on the alignment dependence of moleculesurface reactions yield detailed information on the interaction of molecules with surfaces [1][2][3]. Because the rotational alignment parameter of reacting molecules is connected with the local anisotropy of the potential energy surface (PES), measurements of this parameter in conjunction with theory can lead to the identification of the reaction site [4,5]. Measurement of this parameter as a function of translational energy may also reveal important mechanistic information on, for instance, the importance of orientational steering for reaction [3].The sensitivity of the alignment of reacting molecules to the details of the molecule-surface interaction makes experiments addressing this topic ideal for testing electronic structure theories that attempt to model this interaction. Such tests are highly relevant, and pose huge challenges. About 90% of the chemical manufacturing processes used worldwide employ heterogeneous catalysts [6]. However, the best ab initio theory that can now be used to map out PESs for elementary molecule-surface reactions, density functional theory (DFT) at the generalized gradient approximation (GGA) or meta-GGA level, can provide reaction barriers with an accuracy of no better than 2:2 kcal=mol for gas phase reactions [7]. Even this accuracy has only recently become available [7], and it is therefore not surprising that quantum dynamics calculations using DFT PESs on the rotational quadrupole alignment parameter of H 2 desorbing from metal surfaces such as Pd(100) [8] and Cu(111) [9,10] have not yet been able to quantitatively reproduce the experiments.Dihydrogen-metal surface systems are ideal for testing electronic structure methods as accurate reaction probabilities can be computed within the Born-Oppenheimer (BO) approximation [11]. Making the static surface approximation (neglecting energy transfer involving phonons) should likewise lead to accurate results for low surface temperature (T s ) [12]. Taking advantage of this, it was recently shown that specific reaction pa...

Vibrational deexcitation and rotational excitation of H2 and D2 scattered from Cu(111): Adiabatic versus non-adiabatic dynamics

“…Thus, our calculations cannot account for any possible influence of phonon excitations/deexcitations on the survival probabilities. Here, we should point out that although it has been previously shown 65 that including phonons may lead to absolute values in quantitative agreement with experimental data (when the same surface is considered), the qualitative behavior is essentially the same. Therefore, taking into account this fact and the huge computational cost of including, properly, surface motion, in this work, we stick to the use of surface static approximation.…”

N2 dissociation on W(110): An ab initio molecular dynamics study on the effect of phonons

“…[36,37]. Each sticking probability point has been determined from the computation of a set of 400 NV E trajectories (constant number of atoms, volume and total energy), representing single molecule-surface collisions.…”

“…However, the computational cost of AIMD limited these first studies to a few explorative trajectories. With the growth of computational power and the development of efficient algorithms, the use of AIMD to perform statistically relevant calculations of sticking probabilities for gas-surface reactions has recently become possible [35][36][37]. Advantages of this method lie in the 'on-the-fly' computation of the forces, since this strategy bypasses the need of pre-calculating and fitting a PES, with the possibility to model the effect of surface phonons through the inclusion of the motion of the surface atoms.…”

The effect of the exchange-correlation functional on H2 dissociation on Ru(0001)

“…No large non-adiabatic effects were found in these dynamics calculations, suggesting that the BornOppenheimer approximation works well for these systems. The validity of the static surface approximation has been tested recently for H 2 dissociation on Cu(111) using ab initio molecular dynamics (AIMD) calculations, 39 in which surface atoms in 3 layers of a 2 × 2 unit cell were allowed to move, and static corrugation model (SCM) calculations, 40 which excluded energy exchange with the surface but included the displacement of surface atoms and surface expansion effects. In these studies, good agreement was found between static surface calculations and calculations at the experimental surface temperature (T s = 120 K).…”

“…The surface temperature used in the experiments, T s = 180 K, 31 is rather low. In ab initio molecular dynamics calculations 39 and static corrugation model calculations, 40 almost no effects were found for H 2 dissociating on Cu(111) at a surface temperature T s = 120 K. While the surface temperature for the molecular beam experiments on H 2 dissociation on Ru(0001) was slightly higher, the experimentalists did not find surface temperature effects down to T s = 140 K. 31 Furthermore, the lowest barriers in the H 2 on Ru(0001) system are further away from the surface than was the case for H 2 on Cu(111), suggesting a weaker coupling between H 2 and surface degrees of freedom. Finally, energy exchange is not expected to be important for this system due to the large mass mismatch between a H 2 molecule and a ruthenium atom.…”