Schedule Nov 22, 2002
Testing the accuracy of the xc energy of electronic-strcture theories for real materials -- Example: surface structure and surface chemical reactions at Si (001)
Matthias Scheffler, Fritz-Haber-Institut der Max-Planck
http://www.fhi-berlin.mpg.de/th/member/scheffler_m.html
Recent experiments on the structure of the silicon (001) surface and the dissociative adsorption and associative desorption of H_2 showed that the hitherto trusted understanding of this "simple" system is significantly incomplete. Key words of these studies are: "negative U" and "energy-barrier puzzle". Theoretical results using CI calculations and DFT differ considerably.
This work [see Ref. 1,2] compares the performance of different xc density functionals on surface-clusters and slabs with results obtained by the quantum Monte Carlo (QMC) approach. The results raise warnings on the use of clusters to identify the role of correlation, and also identify limitations of present-day density functionals. We suggest that a correction of the mean-field approach by evaluating correction terms for the xc energy, e.g. by QMC, can be crucial, even for systems where electron correlation is (erroneously) believed to be weak or understood.
Our results also support and explain recent experimental findings.
  1. S.B. Healy, C. Filippi, P. Kratzer, E. Penev, and M. Scheffler, The role of electronic correlation in the Si(100) reconstruction: a quantum Monte Carlo study. Phys. Rev. Lett. 87, 016105 (2001).
  2. Claudia Filippi, Sorcha B. Healy, P. Kratzer, E. Pehlke, and M. Scheffler, Quantum Monte Carlo calculations of H_2 dissociation on Si(001). Phys. Rev. Lett. 89, 166102 (2002).

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