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Manuscript Title: Surface Green's function for a rumpled crystal surface.
Authors: F. Maca, M. Scheffler
Program title: RUMPGF
Catalogue identifier: AADF_v3_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 51(1988)381
Programming language: Fortran.
Computer: CRAY X-MP/24.
Operating system: COS.
RAM: 315K words
Word size: 64
Keywords: Green's function, Crystal field, Density of states, Charge density, Layer kkr method, Multiple scattering, Solid state physics, Condensed matter.
Classification: 7.3.

Nature of problem:
The computer program (as that of paper I) allows to calculate, in any given range of energy E, the Green's function for the one-electron Hamilton operator with a potential for a three-dimensional system with two-dimensional translational symmetry, i.e. a crystal surface or interface. The Green's function satisfies the Bloch-function-type periodic boundary conditions parallel to the surface, for a given value of K and the outgoing-wave boundary conditions normal to the surface. In generalization to paper I, the new code allows to handle rumpled atomic layers, that is, the atoms composing a unit cell may have small differences in heights. Therefore, it is now possible to treat more complex systems, as for example, reconstructed clean surfaces or systems with small adsorbate-substrate distances. I CPC 38(1985)403 and CPC 47(1987)349

Solution method:
The layer-by-layer KKR scheme is used. The crystal (with or without an adsorbate layer) is divided into layers parallel to the surface. All the layers may be rumpled and their two-dimensional unit cell may contain up to four atoms. The potential of each layer is treated in the muffin-tin approximation. The intra-layer scattering is calculated with the method of Kambe, and the inter-layer scattering is calculated using the doubling scheme proposed by Pendry. The Green's function is evaluated in the region of one rumpled layer in a spherical-wave expansion with basis functions centered at the atoms in that layer. Beginning with the top (surface) layer this procedure is repeated layer- by-layer for the specified number of layers. When needed, the Green's function for the bulk layers can also be evaluated.

Restrictions:
All substrate layers are assumed to be identical. They may differ from the top layer. The structure of the top layer must be a superstructure of the substrate, including 1*1. The maximum number of atoms per two- dimensional unit cell in one layer is restricted to four. The maximum array dimensions are set for 45 plane waves and 3 phase shifts (9 spherical waves) per atom.

Running time:
The time for the test run (one energy and one K point) is 5s on a Cray- MP, using 45 plane waves and 3 phase shifts.