PROGRAM SUMMARY
Title of program:
ERWP
Catalogue identifier:
ADOF
Ref. in CPC:
137(2001)415
Distribution format: tar gzip file
Operating system: Unix, Red Hat Linux 6.1, Unicos
High speed store required:
9MK words
Number of bits in a word:
32
Number of lines in distributed program, including test data, etc:
3493
Keywords:
Atom-surface collision, Molecular recombination, Rovibrational
distribution, Reactive scattering, Quantum wave packet,
Pseudospectral scheme, Solid state physics, Collision cascade,
Charge transfer.
Programming language used: Fortran
Computer:
DEC Alpha V6 ,
HP 9000/780 ,
NEC SX5 ,
PC ,
Cray 90 .
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.
Method of solution:
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.
Typical 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.