  We report theoretical results predicting the atomic manipulation of a silver
atom on a Si(001) surface by a scanning probe tip, and providing insight into
the manipulation phenomena. A molecular mechanics technique has been used, the
system being described by a quantum chemistry method for the short-range
interactions and an analytical model for the long-range ones. Taking into
account several shapes, orientations, and chemical natures of the scanning tip,
we observed four different ways to manipulate the deposited atom in a
constant-height mode. In particular, the manipulation is predicted to be
possible with a Si(111) tip for different tip shapes and adatom locations on
the silicon surface. The calculation of the forces during the manipulation
revealed that specific variations can be associated with each kind of process.
These force signatures, such as the tip height signatures observed in scanning
tunneling microscope experiments, could be used to deduce the process involved
in an experiment. Finally, we present preliminary results about the
manipulation in constant-force mode.
