Oscillations around CO atoms seen in STM images

[MisterX]

This effect can be seen in the short film "A Boy and His Atom". I had a couple ideas about what this could be but I am curious if someone knows better.

 

[DrClaude]

They are oscillations in the electron density of surface electrons. Other examples are visible here: http://researcher.watson.ibm.com/researcher/view_group_subpage.php?id=4252

 

[MisterX]

I am curious why this happens. Is it due to the presence of a potential introduced by the CO atom? How can we model this effect to predict the oscillation pattern? How can we model surface electrons, and what is the proper potential to use (1/r or Yukawa? ) for a CO atom?