Book of Abstracts Book of Abstracts - Universität Konstanz

Structural, Electronic and Optical Properties of
Surface saturated Cadmium Sulfide Clusters
Johannes Frenzel 1 , Gotthard Seifert 1 , Jan-Ole Joswig 2 , Michael Springborg 2
1 Institut für Physikalische Chemie, Technische Universität Dresden, D-01062 Dresden, Germany
2 Institut für Physikalische Chemie, Universität des Saarlandes, D-66123 Saarbrücken, Germany
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Due to the quantum-confinement effects the optical properties of cadmium sulfide clusters
tune with respect to their size. In this theoretical work clusters up to 4 nm in diameter, derived
from the electronically almost degenerated crystal structures of cadmium sulfide, wurtzite and
zinc blende (sphalerite), were studied systematically using a simplified LCAO-DFT-LDA
method (DFTB) 1,2 . With a time-dependent extension (TD-DFRT-TB) 2 of this method the optical
spectra of bare and surface saturated cadmium sulfide clusters were calculated. Since there is a
strong dependency of the lowest unoccupied molecular orbitals on structural properties,
basically on the number single-bonded surface atoms the HOMO/LUMO gap trend to zero for
clusters having a large number of single bonded Cadmium atoms 3 . It is shown that effect,
caused by low lying cadmium 5s states, disappears when to these clusters surfactants are added,
namely hydrogen atoms and thiol-groups and their spectra show an asymptotical decreasing of
the HOMO/LUMO gap toward the bulk band gap of CdS while increasing their size.
Figure 1. Structurual shape (left side) and TD-DFRT-TB spectra (right side) of a spherical cadmium sulfide clusters,
unsaturated (dashed curve) and saturated (solid curve).The curves are broadened with Gausians (0.1 eV).
References
[1] Porezag, D. et al., Phys. Rev. B 51, 12947 (1995).
[2] Seifert, G. et al., Int. J. Quantum Chem. 58,185 (1996).
[3] Niehaus, T. et al., Phys. Rev. B 63, 085108 (2001).
[4] Joswig, J.-O. et al., J. Phys. Chem B 107, 2897 (2003).
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