  The Kondo zero bias anomaly of Co adatoms probed by scanning tunneling
microscopy is known to depend on the height of the tip above the surface, and
this dependence is different on different low index Cu surfaces. On the (100)
surface, the Kondo temperature first decreases then increases as the tip
approaches the adatom, while on the (111) surface it is virtually unaffected.
These trends are captured by combined density functional theory and numerical
renormalization group (DFT+NRG) calculations. The adatoms are found to be
described by an S = 1 Anderson model on both surfaces, and ab initio
calculations help identify the symmetry of the active d orbitals. We correctly
reproduce the Fano lineshape of the zero bias anomaly for Co/Cu(100) in the
tunneling regime but not in the contact regime, where it is probably dependent
on the details of the tip and contact geometry. The lineshape for Co/Cu(111) is
presumably affected by the presence of surface states, which are not included
in our method. We also discuss the role of symmetry, which is preserved in our
model scattering geometry but most likely broken in experimental conditions.
