Connecting electronic structure with interatomic potentials: Silicon(111)5x2-gold

One-dimensional systems are predicted to exhibit a variety of exotic phenomena as a result of the fundamental electronic and structural differences with higher-dimensional systems. Specifically, low-dimensional systems are susceptible to a variety of instabilities. It is the aim of this thesis to explore the connections between electronic and structural instabilities by investigating of the Si(111)5x2-Au surface reconstruction and to relate these observations to a larger class of systems including not only noble metals but also transition metals and rare earths.;The 5x2 surface is comprised of an underlying 5x2 chain and a 5x4 dopant superlattice. Recent first-principles total energy calculations determined that the optimal doping corresponds to one adatom per 5x8 unit cell; however, instead of an ordered 5x8 lattice a disordered, half-filled 5x4 lattice is observed experimentally. The surface forms short 5x4 adatom chains separated by adatom-free segments, as observed by scanning tunneling microscopy (STM).;The deviation from the expected 5x8 superlattice to a phase-separated structure is the result of instabilities at the Fermi surface (nesting of the Fermi lines that sit at the zone boundary of a 5x4 unit cell). Mapping of the band structure reveals three distinct bands. The first is completely below the Fermi level and, therefore, does not contribute significantly to the formation of instabilities. The other two bands lie near EF and are prime candidates for triggering the 5x4 superlattice formation since both approach EF at the zone boundaries of a 5x4 unit cell. One band is observed to be metallic, and the other band is semiconducting. It is the competition between the 5x4 potential that is favored by the electronic structure and the doping by the Si adatoms which leads to this phase separation.;The connections between atomic and electronic instabilities can be further extended from noble metals to transition metals and rare earths where d- and f-shell electrons, as well as spin, come into play. Understanding the interactions that result in the structural and electronic instabilities is one of the first steps in engineering new quantum technologies such as an atomic scale memory and nano-electronics.