Effect of surface motion on the rotational quadrupole alignment parameter of D 2 reacting on Cu(111)

Ab initio molecular dynamics (AIMD) calculations using the specific reaction parameter approach to density functional theory are presented for the reaction of D2 on Cu(111) at high surface temperature (Ts = 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 experimentC. Díaz gratefully acknowledges support under MICINN project FIS2010-15127 and CAM program NANOBIOMAGNET S2009/MAT1726. B. Jackson gratefully acknowledges support from the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U. S. Department of Energy, under Grant No. DE-FG02-87ER1374

CHD3 Dissociation on the Kinked Pt(210) Surface: A Comparison of Experiment and Theory

To be able to simulate activated heterogeneously catalyzed reactions on the edge and corner sites of nanoparticles, a method for calculating accurate activation barriers for the reactions is required. We have recently demonstrated that a semiempirical specific reaction parameter (SRP) density functional developed to describe CHD3 dissociation on a flat Ni(111) surface is transferable to describing the same reaction on a stepped Pt(211) surface. In the current work, we compare initial sticking coefficients measured using the King and Wells beam reflectivity technique and calculated from ab initio molecular dynamics trajectories using the same SRP functional for CHD3 dissociation on a kinked Pt(210) surface at a temperature of 650 K. The calculated sticking coefficients overestimate those determined experimentally, with an average energy shift between the two curves of 13.6 kJ/mol, which is over a factor of 3 times higher than the 4.2 kJ/mol limit that defines chemical accuracy. This suggests the SRP functional predicts an activation barrier that is too low for the dissociation on the least coordinated kink atom, which is the site of the lowest energy transition state and where most of the dissociation occurs in the calculations

Incident Angle Dependence of CHD3Dissociation on the Stepped Pt(211) Surface

The dissociation of methane on transition metal surfaces is not only of fundamental interest but also of industrial importance as it represents a rate-controlling step in the steam-reforming reaction used commercially to produce hydrogen. Recently, a specific reaction parameter functional (SRP32- vdW) has been developed, which describes the dissociative chemisorption of CHD3 at normal incidence on Ni(111), Pt(111), and Pt(211) within chemical accuracy (4.2 kJ/mol). Here, we further test the validity of this functional by comparing the initial sticking coefficients (S0), obtained from ab-initio molecular dynamics calculations run using this functional, with those measured with the King and Wells method at different angles of incidence for CHD3 dissociation on Pt(211). The two sets of data are in good agreement, demonstrating that the SRP32-vdW functional also accurately describes CHD3 dissociation at off-normal angles of incidence. When the direction of incidence is perpendicular to the step edges, an asymmetry is seen in the reactivity with respect to the surface normal, with S0 being higher when the molecule is directed toward the (100) step rather than the (111) terrace. Although there is a small shadowing effect, the trends in S0 can be attributed to different activation barriers for different surface sites, which in turn is related to the generalized co-ordination numbers of the surface atom to which the dissociating molecule is adsorbed in the transition state. Consequently, most reactivity is seen on the least co-ordinated step atoms at all angles of incidence

Application of van der Waals functionals to the calculation of dissociative adsorption of N 2

Theoretical Chemistr

N 2

Theoretical Chemistr

Highly efficient activation of HCl dissociation on Au(111) via rotational preexcitation

NWOTheoretical Chemistr

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

The following article appeared in Journal of Chemical Physic 137.6 (2012): 064707 and may be found at http://scitation.aip.org/content/aip/journal/jcp/137/6/10.1063/1.4742907We have studied survival and rotational excitation probabilities of H2(vi = 1, Ji = 1) and D2(vi = 1, Ji = 2) upon scattering from Cu(111) using six-dimensional (6D) adiabatic (quantum and quasi-classical) and non-adiabatic (quasi-classical) dynamics. Non-adiabatic dynamics, based on a friction model, has been used to analyze the role of electron-hole pair excitations. Comparison between adiabatic and non-adiabatic calculations reveals a smaller influence of non-adiabatic effects on the energy dependence of the vibrational deexcitation mechanism than previously suggested by low-dimensional dynamics calculations. Specifically, we show that 6D adiabatic dynamics can account for the increase of vibrational deexcitation as a function of the incidence energy, as well as for the isotope effect observed experimentally in the energy dependence for H2(D2)/Cu(100). Furthermore, a detailed analysis, based on classical trajectories, reveals that in trajectories leading to vibrational deexcitation, the minimum classical turning point is close to the top site, reflecting the multidimensionally of this mechanism. On this site, the reaction path curvature favors vibrational inelastic scattering. Finally, we show that the probability for a molecule to get close to the top site is higher for H2 than for D2, which explains the isotope effect found experimentallyThis work has been financially supported by the DGI (Project Nos. FIS2010-15127 and FIS2010-19609-C02-02), the CAM (Project No. 2009/MAT1726), the Basque Dpto. de Educación, Universidades e Investigación, and the UPV/EHU (Project No. IT-366-07

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

Theoretical Chemistr

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

The following article appeared in Journal of Chemical Physic 134.11 (2011): 114708 and may be found at http://scitation.aip.org/content/aip/journal/jcp/134/11/10.1063/1.3567397Based on a slab model of H2 dissociation on a c(2 * 2) structure with Ti atoms in the first and third layers of Al(100), a six-dimensional (6D) potential energy surface (PES) has been built. In this PES, a molecular adsorption well with a depth of 0.45 eV is present in front of a barrier of height 0.13 eV. Using this PES, H2 dissociation probabilities are calculated by the classical trajectory (CT), the quasiclassical trajectory (QCT), and the time-dependent wave-packet (TDWP) method. The QCT study shows that trajectories can be trapped by the molecular adsorption well. Higher incident energy can lead to direct H2 dissociation. Vibrational pre-excitation is the most efficient way to promote direct dissociation without trapping. We find that both rotational and vibrational excitation have efficacies close to 1.0 in the entire range of incident energies investigated, which supports the randomization in the initial conditions making the reaction rate solely dependent on the total (internal and translational) energy. The H2 dissociation probabilities from quantum dynamics are in reasonable agreement with the QCT results in the energy range 50-200 meV, except for some fluctuations. However, the TDWP results considerably exceed the QCT results in the energy range 200-850 meV. The CT reaction probabilities are too low compared with the quantum dynamical resultsThe research of J.C.C. is supported by the Marie Curie Research Training Network HYDROGE