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@ARTICLE{Krieger:1055123,
      author       = {Krieger, Ina and Sokolowski, Moritz and Haags, Anja and
                      Bredow, Thomas and Kumpf, Christian and Tautz, F. Stefan and
                      Held, Georg},
      title        = {{S}tructure analysis of {PTCDA}/{A}g(100) by low-energy
                      electron diffraction and density functional theory},
      journal      = {Physical review / B},
      volume       = {113},
      number       = {7},
      issn         = {2469-9950},
      address      = {Woodbury, NY},
      publisher    = {Inst.},
      reportid     = {FZJ-2026-01872},
      pages        = {075425},
      year         = {2026},
      abstract     = {The adsorption geometry of the planar 3, 4, 9,
                      10-perylene-tetracarboxylic-dianhydride (PTCDA) moleculein
                      the commensurate c(8 × 8) structure on Ag(100) was
                      determined from the analysis of the intensities in
                      low-energy electron diffraction (LEED-IV). Using data from
                      different angles of incidence and optimized computercode, we
                      were able to overcome earlier challenges given by the
                      limitations of the experimental data set and thecalculation
                      times required for the large unit cell with many atoms.
                      Testing of different structures confirmed theon-top
                      adsorption site for the center of the perylene core. The
                      final Pendry R factor of RP = 0.180 for the on-topposition
                      is significantly lower than the one for the fourfold hollow
                      position (minimum RP = 0.369) that is henceexcluded. The
                      molecule shows archlike deformation with a downshift of the
                      terminal carboxylic groups. Boththe molecular structure and
                      the adsorption height are in very good agreement with
                      results from an earlier normalincidence x-ray standing wave
                      (NIXSW) experiment and new density functional theory (DFT)
                      calculations,which we performed in parallel for 0 K and in
                      addition for 300 K. The LEED-IV analysis demonstrates that
                      thePTCDA induces a relaxation (−0.08 versus −0.04 Å of
                      the clean surface) and buckling (0.33 Å) of the topmostAg
                      layer. Special attention was given to the Ag atom below the
                      central ring of the PTCDA. The IV analysiswas rather
                      insensitive to its vertical position, and a small R factor,
                      close to the minimal, was also obtainedwhen this Ag atom was
                      moved upward (RP = 0.185) or even an Ag vacancy site (RP =
                      0.171) was assumed.However, these structures could be
                      excluded on the basis of DFT calculations. The vacancy
                      structure has afree adsorption energy that is 0.18 eV larger
                      compared to the favored geometry where this central Ag atom
                      ispushed downward, partly due to the energy cost for the
                      vacancy formation. The discussion of
                      adsorbate-inducedformation of vacancy sites is important
                      because it was reported for C60 on Ag(111). The up- and
                      downwarddisplacements of the first-layer Ag atoms support
                      the understanding of the chemical bond of the PTCDA tothe Ag
                      substrate and reveal how the originally planar π system is
                      locally distorted. Our analysis proves thatLEED-IV is a
                      powerful technique for surface crystallography of large
                      organic adsorbates.},
      cin          = {PGI-3},
      ddc          = {530},
      cid          = {I:(DE-Juel1)PGI-3-20110106},
      pnm          = {5213 - Quantum Nanoscience (POF4-521)},
      pid          = {G:(DE-HGF)POF4-5213},
      typ          = {PUB:(DE-HGF)16},
      doi          = {10.1103/gxh1-b3w4},
      url          = {https://juser.fz-juelich.de/record/1055123},
}