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

L. Spiess, A. J. Freeman, P. Soukiassian

Research output: Contribution to journalArticle

35 Citations (Scopus)

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 - Jan 1 1994

ASJC Scopus subject areas

  • Condensed Matter Physics

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