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Manuscript Title: Nonreactive atom/molecule-surface scattering within the finite basis wave packet method.
Authors: D. Lemoine
Program title: FBWPSURF
Catalogue identifier: ADDR_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 97(1996)331
Programming language: Fortran.
Computer: HP 9000 Series 715.
Operating system: UNIX, UNICOS.
RAM: 1.2M words
Word size: 32
Keywords: Solid state physics, Molecule-surface, Collision cascade, Diffractive scattering, Rotational excitation, Quantum wave packet, Finite basis, Representation, Pseudospectral scheme, Elastic.
Classification: 7.10, 16.7.

Nature of problem:
The scattering matrix and transition probabilities are computed for the nonreactive collisions of closed-shell atoms or diatomic molecules with a rigid surface. The inelastic channels which are considered are the diffractive scattering and the rotational (de-) excitation for a diatomic collider. The surface unit cell has the general form of a parallelogram. One may appropriately reduce the dimensionality by defining either a 1D vs a 2D corrugation or a flat surface.

Solution method:
The time-dependent wave function of the collider is expanded in terms of the asymptotic eigenfunctions. The resulting finite basis representation (FBR) consists of a direct product of plane waves for the translational motion and of a nondirect product of spherical harmonics for the angular degrees of freedom [1, 2]. The wave function is propagated in time owing to the Chebychev scheme [3], in the FBR where the kinetic energy operator is diagonal. Potential matrix elements are efficiently evaluated in a pseudospectral way by means of sequential 1D transformtions of the wave function between momentum and coordinate spaces. Fast Fourier transforms are performed for the translational and azimuthal coordinates whereas a Gauss-Legendre transform is used for the polar coordinate. Additionally, FBWPSURF makes use of various techniques: floating grid and adjustable basis [4], efficient cutoff procedure and simplified asymptotic treatment [2]. The initial wave function is chosen to be a Gaussian distribution along the surface normal, corresponding to a range of energies over which a post- collisional analysis can be performed [5].

Running time:
5.5 s (160 s) on a Cray 98 (Silicon Graphics R 4400 Indigo) for the test run.

[1] G.C. Corey, J.W. Tromp and D. Lemoine, in: Numerical Grid Methods and Their Application to Schrodinger's Equation, edited by C. Cerjan (Kluwer Academic, Dordrecht, 1993) p. 1.
[2] D. Lemoine, J. Chem. Phys. 101(1994)10526.
[3] H. Tal-Ezer and R. Kosloff, J. Chem. Phys. 81(1984)3967.
[4] D. Lemoine and G.C. Corey, J. Chem. Phys. 92(1990)6175.
[5] R.C. Mowrey and D.J. Kouri, Comp. Phys. Commun. 63(1991)100.