Topic 5. Analytic bond order potentials (BOP) for enhanced MD simulations:

As mentioned in the applications of empirical molecular dynamics to structure relaxations (topics: bonded interfaces , quantum structures , and glasses ) the results depend strongly on the quality of the interatomic potentials used. A second problem is the electronic structure, which is not included in simple empirical potentials, thus e.g. not applicable in image calculations for TEM and electron holography as discussed in the chapter direct object retrieval . Bond order potentials, developed on the tight-binding approximation by David Pettifor and his group in Oxford , and justified by coarse graining methods from ab initio principles, allow to enhance the empirical MD, as it preserves the essential quantum nature of atomic bonding, yet abandons the electronic degree of freedom. (cf. e.g. Fig.1 and /1/). /2/, (Fig. 3). Figs. 4-6.

Newer results (since 2007) may be found at the reconstructed start pages: Particles/Glass        QD/QW        Waferbonding        BOP&HREM     
which are related to the topics of the experimental departement II
via the research topics: nanowires-nanoobjects      silicon-photonics-photovoltaics      interfaces-and-material-systems     

Fig.1 (166Kb): Spontaneous Si-(100) surface dimerization and sigma-pi bond exchange with the BOP4+ after 1ns annealing with the 600K maximum temperature (for details cf.movie, avi-type,28Mb , a movie showing the BOP4 bond stability movie, MPEG,0.8Mb , and the MPI-annual report /1/).

Fig.2 (53Kb): Bond order terms used in the Tersoff potential versus the derivation of the analytical form of the bond order potentials.

Fig.3 (1.3Mb): Application of the BOP to TEM image simulations: /4-6/

References (selected, links partially restricted, see also MPI-Publications and Personal References , paper&books , proceedings&talks

• /2/ Conrad D. and K. Scheerschmidt : Empirical bond-order potential for semiconductors.
  Phys. Rev. B 58, 4538-4542 (1998) (PDF 333Kb) (Bib-link)
• /3/Conrad, D., K. Scheerschmidt and U. Gösele, On the possibility of diamond wafer bonding in ultrahigh vacuum,
  Appl. Phys. Letters 77 (2000)49-51.printed paper (PS 182Kb)
• /4/ Scheerschmidt K., D. Conrad, A.Y. Belov, and D. Timpel, Enhanced semi-empirical potentials in molecular dynamics simulations of wafer bonding
  Materials Science in Semiconductor Processing, 3 (2000) 129-135. extended paper of EMRS99, Strasbourg (PS, 6Mb)
• /5/ K. Scheerschmidt, D. Conrad, Y. Wang, Tight-binding-based potentials: molecular dynamics of wafer bonding.
  Computational Materials Science 22,56-61 (2001) (PDF, 333Kb)
• /6/ V. Kuhlmann: Entwicklung eines semi-empirischen Potentials für die molekulardynamische Simulation von Nanostrukturen
  Dissertation (2006) (PDF, 4.3Mb)

Recent and additional conference papers, posters and drafts (partially local acces only):

• BOP4presentation Optimization of BOP4+ parameter PPS (607Kb)
• DFTEM 2006 Wien extended abstract, (PDF 208Kb) or Poster, (PS 27Mb)
• IMC2006 Sapporo extended abstract, (PDF 512Kb)

Cooperation and related links:

Links to the other topics of MD group:

Kurt Scheerschmidt, HomePage, Email, 11.1.11