The mechanical behavior of short atomic chains under the action of a scanning tunneling microscope (STM) tip is investigated from computerized simulations. The calculation of the constrained atomic positions is performed with a molecular-dynamics approach. The system studied consists of $N(1\mathrm{}<~N<~5)$ xenon atoms located in the Cu(110)-surface/tetragonal Cu-tip interface. The tunneling current calculation is based on the elastic scattering quantum chemistry method. The combination of these two descriptions (electric and mechanical) allows the behavior of the adsorbates to be described precisely. In particular, when working in the operational constant current mode, our numerical scheme behaves as a realistic virtual STM that allows an accurate prediction of the intrinsic mechanisms involved in similar experiments. In a first stage, for a single atom we present a diagram summarizing the different possible mechanisms versus the different initial conditions. By adding a second adsorbate, we establish a relation between the adsorbate spacing and the evolution of the tip trajectory [the so-called feedback loop signal (FLS)]. Finally, we present a discussion on the shape of such FLS signals when a linear chain composed of five Xe atoms is laterally pushed by the tip. The extraction of quantitative information on the adsorbate configurations during the manipulation is also addressed.

• Received 4 July 2000

DOI:https://doi.org/10.1103/PhysRevB.63.085415