Stepanyuk et al. observed formation of long Co chains on Cu(111) at 0.006 ML coverage at 20 K. Their results are in good agreement with both Korringa-Kohn-Rostoker (KKR) scattering theory. The former, however, predicts rapid decrease in interaction energy below 5 Å distance between two Co atoms, while experimental data suggests an opposite trend (Fig. ). We think that such behavior might be related to the fact that KKR theory does not account for bulk electronic states. The interaction energy is, however, decaying at an expected 1/r -2 rate. Interestingly, the presented STM also shows that Co chains are at a distance of third or fourth interaction energy minimum (Fig. (a)).