Berechnung von Stufenkanten auf der As-bedeckten Si(111)-Oberfläche mit einem parallelisierten ab initio Programm

The first part of this thesis presents the parallelisation of the EStCoMPP-code (EStCoMPP is an acronym for "Electronic Structure Code for Materials Properties and Processes"). Using Density-Functional-Theory EStCoMPP simulates many electron systems, found in molecules and solids and computes characteristics of their groundstate. The program employs periodic supercells to approximate inhomogeneous systems. The DFT accounts for the electron-electron interaction by means of a one-electron-potential that depends on the electron-density which is determined selfconsistently. The interaction of valence-electrons with ionic cores is described by norm-conserving pseudo potentials. The electronic states are numerically calculated by solving an eigenproblem for a set of k-points to find the v=1...M eigenstates with the lowest energies. These eigenstates are represented in a basis of plane-waves labeled by G-vectors of the reciprocal lattice. Corresponding to the indices k, v and G of the coefficients of the wavefunctions three parallelisation strategies are considered, each allocating partial ranges of the respective index to individual processors. The k-point-parallelisation is highly efficient since eigenproblems assigned to different k-points can be solved independently, thus only 0.2% of the computing time account for non-parallelized tasks. In combination with the G-vector-parallelisation performance scales well with the number of processors for large systems. For a supercell containing with 110 Atoms less than 0.4% of computing time is spent in unparallelized routines. The second part of this thesis utilizes the EStCoMPP-code to investigate step-edges on As-covered Si(111)-surfaces. The total energies and structures of several metastable states are calculated by relaxing given starting configurations. Since the amount of As contained in the step-edges varies for different structures, the formation energies of the respective step-edges depend on the reference-energy that is used as chemical potential for As. For As-bulk as well as As_4 as reference the most stable structure found was the (11-2)-step-edge with all exposed Si-atoms at the step-edge replaced by As. Based on the total energies of the various step-edges the form of As-covered Si-islands with the lowest overall energy is predicted by two-dimensional Wulff-plots. Using As_4-molecules as reference we find triangular islands terminated by (11-2)-step-edges. For As-bulk as reference the result are six-sided islands terminated alternately by short (-1-12)-edges and long (11-2)-edges. The available STM-pictures for Si-homoepitaxy don't show islands in equilibrium so that the predictions of these calculations could not be compared to experimental data.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2002

Author dc:creator

• Berger, Ralf

Contributors dc:contributor

• Schroeder, Kurt

• info:eu-repo/classification/ddc/530
• Silicium
• Kristallfläche
• Arsen
• Adsorptionsschicht
• Ab-initio-Rechnung
• Physik
• As/Si(111)
• Stufenkanten
• DFT
• Dichtefunktionaltheorie
• EStCoMPP
• Parallelisierung

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123549%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:61941