Ge(100) 2×1 and c(4×2) surface reconstructions studied by ab initio total-energy molecular-force calculations

L. Spiess, Arthur J Freeman, P. Soukiassian

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Abstract

The 2×1 and c(4×2) surface reconstructions on Ge(100) are investigated by the ab initio, all-electron, molecular-cluster method, which solves the local-density-functional equations and provides analytical energy gradients. We use finite-size clusters (up to 71 atoms including 39 Ge atoms) to model the Ge(100) surfaces. Atomic-force calculations are extensively used to obtain the minimum-energy geometry for the different structures investigated. We determine and compare the binding energy and geometry up to the fourth layer of the symmetric (2×1), buckled (2×1), as well as the higher-order c(4×2) reconstruction. Important energetic and structural differences are found compared to the corresponding Si(100)2×1 surface. The asymmetric dimer model is found to be 0.34 eV/dimer lower than the symmetric one with the up-dimer atom being 0.19 above the plane of the unreconstructed surface and a dimer tilt of 15°. The buckled 2×1 and c(4×2) reconstructions are found to be close in energy, which suggests that both could be present on the surface at room temperature. These results are in excellent agreement with scanning-tunneling-microscopy experiments and previous theoretical studies using a slab geometry. This energy is well below the energy of the symmetric dimer reconstruction indicating that dimer flipping recently suggested for the Si(100)2×1 surface is unlikely to occur in the case of the Ge(100) surface. In significant contrast to the Si(100) surface, we found that the Ge-Ge dimer is weaker with bond lengths that are slightly above the bulk value of 2.44, at 2.48 and 2.50 for the asymmetric 2×1 and c(4×2) reconstructions, respectively. It suggests that the Ge(100) surface might show some different behavior towards adsorption.

Original languageEnglish
Pages (from-to)2249-2258
Number of pages10
JournalPhysical Review B
Volume50
Issue number4
DOIs
Publication statusPublished - 1994

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Surface reconstruction
Dimers
dimers
energy
Atoms
Geometry
geometry
atoms
Bond length
Scanning tunneling microscopy
molecular clusters
Binding energy
scanning tunneling microscopy
slabs
binding energy
Adsorption
Electrons
gradients
adsorption
room temperature

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Ge(100) 2×1 and c(4×2) surface reconstructions studied by ab initio total-energy molecular-force calculations. / Spiess, L.; Freeman, Arthur J; Soukiassian, P.

In: Physical Review B, Vol. 50, No. 4, 1994, p. 2249-2258.

Research output: Contribution to journalArticle

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