Density functional theory investigations of surface structure and surface stress in adsorbate layers on Cu, Pd and Ir surfaces

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Abstract

An introduction to surface structure and plane wave density functional theory (DFT) is presented
along with theoretical studies of seven adsorbate systems.
A new energetically favourable structure of low symmetry is found for furan on Pd(111)
that is entirely consistent with previous experimental findings from scanned-energy mode photoelectron
diffraction (PhD). In addition, it is found that the C3H3 decomposition product of
furan on the same surface is likely to be adsorbed in a propargyle conformation (CH-C-CH2)
although some cooccupation of the molecule in a half benzene conformation (CH-CH-CH) is
also possible.
Methoxy is found to adsorb at local short bridge sites only on Cu(110), occupying locations
both above the clean surface and above pairs of surface Cu adatoms. Simulated scanning
tunneling microscope (STM) images of the (5×2) reconstruction are found to be in qualitative
agreement with previous images recorded experimentally. The experimentally determined local
structure of cytosine on the same surface is confirmed and models are proposed for the (6×6)
reconstruction.
An increased tensile surface stress is found to be associated with the Ir(001)(1×1) !
Ir(001)(5×1)-hex phase transition, thus confirming that the reconstruction is not a consequence
of the large surface stress of bulk terminated Ir(001). In contrast, H adsorption on
Ir(001) (5×1)-hex does lead to a reduction of the surface stress in the range 1.76-2.06 Nm−1
for a H coverage range 0.6-0.8 ML in excellent agreement with the experimentally-determined
value of 1.7 Nm−1.
The energetically favourable structure for methanethiolate adsorption on Cu(100) is found
to be a c(6×2) missing row structure that allows effective relief of surface stress. On Cu(111)
several complex overlayer models for methanethiolate adsorption have similar associated surface
energy, suggesting that the local structure is dependent on the availability of Cu adatoms.
For adsorption on both surfaces, agreement with previous STM images and MEIS results is
discussed.

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