Structure and dynamics of low-dimensional systems

I studied structural and dynamical properties of low dimensional systems using numerical approaches at different levels of sophistication. I focused my interest on the physical phenomena associated with the interaction of atoms with surfaces. I studied two topics which are intimately connected with this interaction. One of them is a procedure to quantitatively interpret atomic force microscopy (AFM) images of solid surfaces. The other topic is the effect of adsorbate on structural, electronic and dynamical properties of the substrate.;When studying theory for the AFM, I considered a model system consisting of a Pd metal tip probing the graphite surface. Using ab initio density functional theory (DFT), I calculated the interaction between this Pd AFM tip and graphite and mapped it onto a parameterized energy functional. The calculation of AFM tip trajectories at different loads revealed that atomic resolution is only achievable for loads exceeding 5 ;I selected H/Pd as the model system to study the effect of adsorbate on the structural and dynamical properties of the substrate. I based the description of the H-Pd system on density functional calculations, which were subsequently mapped onto a parametrized many-body alloy Hamiltonian. Using this Hamiltonian, I calculated the equilibrium structure of the clean and hydrogen covered Pd (001) and Pd (110) surfaces, as well as the corresponding surface phonon spectra. The most pronounced effect of hydrogen is a strong softening of the Rayleigh wave on Pd (001), which is indirectly related to "hydrogen embrittlement" observed in the bulk. I addressed this latter problem using molecular dynamics. I studied the equilibrium structure, elastic properties, and in particular the mechanical breakdown of bulk Pd under tensile stress, as a function of temperature and hydrogen concentration. My results indicate that the microscopic origin of "hydrogen embrittlement" is an increased ductility and plasticity in regions saturated by hydrogen, in agreement with the postulated Hydrogen Enhanced Local Plasticity mechanism.