Electronic structure calculations of the stability of silver ultra-thin films and effects of derivatives on oligomer structures

Computational modeling has become a powerful tool in materials science and engineering. With the rapid growth in the power and speed of modern computers, larger and more realistic systems are able to be modeled. Quantum mechanical simulations are among some of the most accurate techniques to study solids and molecules. These techniques are computationally very expensive but have been extended to larger systems by clever approximations.; Electronic structure calculations have been applied to the study of Ag ultra-thin films on III--V substrates. Silver usually forms islands on the semiconductor surface when initially deposited under room temperature conditions. This is contradicted by recent experiments that have shown that flat atomic layers can be grown by passing the Ag overlayers through a different kinetic pathway. Through this different kinetic path, Ag shows a preferential stability that is dependent on how much Ag is initially deposited onto the substrate. The preferential stability of the film has been attributed to quantum confinement of the electrons in the metallic overlayer and this claim has been supported by simple calculations. First principles density functional theory calculations have been used in this dissertation to examine the preferential stability of the overlayer and examine the quantum confinement of the electrons in the film. The first principles calculations show the importance of the atomic structure of the metal layer, which is not accounted for in the simple electron gas calculations performed earlier.; Another challenge in materials science is to tailor make materials with particular characteristics. Organic molecules have been shown to emit light in the visible range and there has been intense research into using these materials for many new applications. Semiempirical Hartree-Fock techniques are used to calculate properties of a large class of polymers. Both the molecular structure and electronic structure are analyzed. It is found that the geometries the substitutions induce is as important as the effects of the substitutions themselves. Steric repulsions cause some oligomers to deviate from a planar configuration. This is known to have detrimental on the luminescent efficiency of the molecule. Emission estimates are made from some of the planar molecules.