Abstract:The reaction of H 2 on Cu͑100͒ is investigated using a four-dimensional ͑4D͒ quantum dynamical fixed-site model to assess the influence of molecular rotation on dissociation over the most reactive ͑the bridge͒ site. The potential energy surface ͑PES͒ is a fit to the results of density functional calculations performed using a generalized gradient approximation treating a Cu slab with a periodic overlayer of H 2 . Dissociation probabilities for molecules with ''helicoptering'' (m j ϭ j) and ''cartwheeling'' ͑m … Show more
“…The 2D results are for fixed impact and orientation, the molecule following the most favorable dissociation route found for the high symmetry sites [17]. Four-dimensional results are given for a model which includes parallel translational motion but excludes rotations [8], and for a so-called fixed-site (bridge) model, which includes rotations [9]. The results confirm [10] all six degrees of freedom affects the reaction, and that all six degrees of freedom should be taken into account in the calculation of reaction probability.…”
mentioning
confidence: 99%
“…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.…”
mentioning
confidence: 99%
“…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.…”
mentioning
confidence: 99%
“…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][7][8][9], though 6D calculations have been done in a mixed quantum-classical framework [20].…”
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...
“…The 2D results are for fixed impact and orientation, the molecule following the most favorable dissociation route found for the high symmetry sites [17]. Four-dimensional results are given for a model which includes parallel translational motion but excludes rotations [8], and for a so-called fixed-site (bridge) model, which includes rotations [9]. The results confirm [10] all six degrees of freedom affects the reaction, and that all six degrees of freedom should be taken into account in the calculation of reaction probability.…”
mentioning
confidence: 99%
“…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.…”
mentioning
confidence: 99%
“…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.…”
mentioning
confidence: 99%
“…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][7][8][9], though 6D calculations have been done in a mixed quantum-classical framework [20].…”
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...
“…In Figure , the 6D results are compared to results of several low-dimensional models, using essentially the same PES (actually the low-dimensional calculations used PES-II and the 6D calculations PES-III, but the low-dimensional results should not differ much for PES-II and PES-III). The 2D results are for fixed orientation and impact site, for the most favorable bridge-to-hollow dissociation route. , Four dimensional results are given for two models, one including parallel translations but excluding rotations, , and one for the so-called fixed site bridge model incorporating rotations but excluding parallel translations. , The comparison confirms the conclusion of 6D classical trajectory calculations 120 that motion in all six molecular degrees of freedom importantly affects the reaction of H 2 on metal surfaces, and that for quantitative accuracy, motion in all six degrees of freedom should be taken into account. 17 The 6D probability for dissociation of H 2 on Cu(100) is shown as a function of E n (solid line), also comparing with results of 2D calculations (dot−dashed line), , 4D calculations including parallel translation (dotted line) 154 and 4D calculations including rotational motion (dashed line). , From refs and .…”
We consider the scattering of H2 from surfaces for two benchmark systems. The system H2 + LiF(001) is the
classical example of hydrogen scattering off an ionic surface. Quantum dynamical calculations employing a
new model potential and experiments have shown that the electrostatic interaction between the molecule's
quadrupole moment and the surface ions has a crucial influence on the scattering in this system. The results
suggest that the ionicity of the surface ions in ionic surfaces can be probed by scattering H2 of these surfaces,
for instance, by measuring the differences between diffraction of cold p-H2 and cold o-H2. The system H2 +
Cu is the classic example of activated dissociative chemisorption. It is now possible to perform quantum
dynamical calculations on fully activated dissociative chemisorption in which all molecular degrees of freedom
are treated without dynamical approximations, as here illustrated for H2 + Cu(100). This development makes
it possible to evaluate the accuracy of electronic structure methods for molecule−surface interactions, to help
interpret trends in the reactivity observed experimentally, and to arrive at new predictions for experiments.
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