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Manuscript Title: Quantum wave packet approach to the Eley-Rideal reactive scattering between a gas phase atom and an adsorbate.
Authors: D. Lemoine, B. Jackson
Program title: ERWP
Catalogue identifier: ADOF_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 137(2001)415
Programming language: Fortran.
Computer: DEC Alpha V6, HP 9000/780, NEC SX5, PC, Cray 90.
Operating system: Unix, Red Hat Linux 6.1, Unicos.
RAM: 9M words
Word size: 32
Keywords: Atom-surface collision, Molecular recombination, Rovibrational distribution, Reactive scattering, Quantum wave packet, Pseudospectral scheme, Solid state physics, Collision cascade, Charge transfer.
Classification: 7.10, 16.8.

Nature of problem:
Reaction cross sections and product rovibrational (nu,j) distributions are computed for the direct-impact {A + BS(nu) => AB(nu,j) + S} molecular recombination process, where initially, A is a gas phase atom, B an atom adsorbed onto a substrate S, and nu indexes the quantum state of the adsorbate vibration with respect to the surface.

Solution method:
The partial wave expansion technique is employed in cylindrical coordinates within the flat-surface, rigid-substrate approximation, thereby reducing the full treatment to three-dimensional (3D) numerical resolutions [1]. The coordinate system retained involves the distance of the diatom center of mass to the surface and the diatom separations along axes normal and parallel to the surface. A pseudospectral quantum wave packet approach is implemented. The time-dependent wave function is expanded in terms of the Laplacian eigenfunctions. The time evolution relies on the split operator propagator [2] and the Hamiltonian operation proceeds via 1D sequential transformations between coordinate and momentum spaces. Fast Fourier transforms are performed for the two Cartesian coordinates whereas an orthogonal discrete Bessel transform [3] is applied for the cylindrical radius. The initial wave function consists of the product of a Gaussian wave packet for the motion of the incident atom normal to the surface, of a plane wave for its parallel motion, and of a Morse state for the adsorbate vibration. The interaction potential model is chosen to be of the LEPS [4] functional form. Optimized absorbing boundary conditions [5] are enforced in all outgoing channels in order to achieve the minimal configuration space representation. Energy-resolved flux analysis [6] in the molecular region yields reaction cross sections and rovibrational distributions over the incoming energy range. The program uses libraries BLAS, LAPACK and selected FFT packages.

Running time:
168 s (44/51 mn) on one NEC SX5 (DEC Alpha V6) processor for the test run with 64 (32/64) bit words.

References:
[1] M. Persson, B. Jackson, J. Chem. Phys. 102 (1995) 1078.
[2] M.D. Feit, J.A. Fleck Jr., A. Steiger, J. Comput. Phys. 47 (1982) 412.
[3] D. Lemoine, Comput. Phys. Commun. 99 (1997) 297.
[4] J.H. McCreery, G. Wolken Jr., J. Chem. Phys. 67 (1977) 2551.
[5] U.V. Riss, H.D. Meyer, J. Chem. Phys. 105 (1996) 1409.
[6] J. Dai, J.Z.H. Zhang, J. Phys. Chem. 100 (1996) 6898.