Simulating unusual phenomena in low dimensional systems

Abstract

"This thesis deals with physics phenomena in low dimensional systems, i.e., systems that range between few atoms and the bulk. The work deals with well studied (in this sense, classical) phenomena such as quantum tunneling and the enhancement of tunneling, surface reconstructions on surfaces, stability of structures vs. shape and size of nanoparticles, the mechanical properties studied in classical elastic theory for metals (such as hardness, ductility, malleability, etc.). However, althouh we have used and applied "classical" theories from both quantum and mechanical physics, we studied new, unusual phenomena in low dimensional systems. Thus, the reader will find in this thesis work, theoretical developments, hypothesis and results that advance explanations in unusual physical phenomena. In quantum physics there are phenomena which do not have analogs in classical physics. One of these phenomena is quantum tunneling. The manifestation of this process is penetration of a particle or more complicated object through a potential barrier. Such process is forbidden by classical mechanics. Besides tunneling through static potential barriers there are many phenomena in labs and nature when tunneling occurs across nonstationary barriers. There are many examples of such processes, ionization of atoms by a nonstationary electric filed, ac electric current in junctions of metals or semiconductors, dissociation of molecules by a high-frequency fields, field emission from metals by the action of an ac field, decay of current states in Josephson junctions, alpha decay of nuclei initiated by an external flux of protons, etc. These processes of tunneling through nonstationary barriers require an adequate theoretical description. Regarding studies for nanoparticles, we have faced the shape, structure and mechanical properties of metallic nanoparticles. First, we studied a particular truncation operated on the regular icosahedron gives rise to a new (not reported before) particle with five-fold symmetry and external decahedral shape termed the decmon motif. These truncated icosahedra exposes internal facets (100) and (111)â˘AS¸ additional to the external (111) facets of the regular icosahedron. The uncovering of additional facets to the icosahedron gives rise to phenomena such as surface reconstructions and a delicate competition in the energy contribution coming from the new facets (100) and (111) to the total surface energy."