  Atoms or pairs of ions picked up by probe tips used in dynamic force
microscopy (DFM) can be strongly displaced and even hop discontinuously upon
approach to the sample surface. The energy barriers for some of those hops are
of the right order of magnitude to explain the rise in energy dissipation
commonly observed in DFM measurements at room temperature. The systematic
computations reported here can explain the infrequent jumps and very low
average energy dissipation observed low temperature in a previous DFM study on
a KBr(001) sample. Close to the surface we indeed find new states separated by
small energy barriers which account for those phenomena. These energy barriers
strongly depend on details of the atomic arrangement in the vicinity of the tip
apex.
