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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.

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.