|Abstract: ||The cadmium yellow paints used in impressionist and modernist paintings in early
1900s are undergoing several deterioration processes, including whitening and discoloration.
Relevant e↵ects produced at the surface of modern paintings include the
growth of discolored crusts, formed mainly by white globular hydrated cadmium sulfate
CdSO4*nH2O and cadmium carbonate (CdCO3 ). In view of the fact that the
pigment, cadmium sulfide, was historically synthesized by means of dry and wet processes
and that CdCO3 and CdSO4 are reagents for this procedure, their identification
alone does not constitute conclusive proof of photo-oxidation. The origins of such
chemical and physical alterations are still under debate.
Structural defects in CdS, among other possible causes like photo-oxidation processes,
may play a role in the degradation process. Their presence in the pigment surface
alters the electronic structure of cadmium sulfide by forming acceptor levels in the gap
of the semiconductor. Such levels make the surface more reactive in the interaction
with external agents (oxygen, water ...).
To this end, we present a theoretical study of points defects, namely Cd- and S- vacancies,
in the structural wurtzite structure (bulk) and [10¯10] CdS surface. In order to
understand, at atomic level, the oxidation and hydration mechanisms of these whitish
globules, we present the early stages of the interaction between the hexagonal clean
and defective [10¯10] surface of CdS and O2 and H2O molecules to simulate the combined
e↵ects of exposure to air and humidity.
The geometrical and electronic structures as well as the vacancy formation and adsorption
energies are determined with the use of a first principles method. All the
calculations are performed within the framework of the Density Functional Theory
(DFT) in the Generalized Gradient Approximation (GGA-PBE) with the use of ultrasoft
pseudopotentials. Despite the standard DFT-GGA ensures a correct order of
electronic states, the G0W0 calculations are strongly required to attribute an accurate position of the trap level.
Considering the possibility to investigate in a broader spectral range, such theoretical
method would be helpful in the interpretation of experimental evidences on fluorescence
emissions produced from by yellow altered. This thesis highlights the key role
that first-principles methods can play in the application of materials science to art