[Wien] Surface Wavefunction Oscillating

[Chiung-Yuan Lin]

Dear all,
  Has anyone seen that the wavefunction in the vacuum region
of a surface starts from some smooth exponential decay
and then becomes oscillatory?
  I am working on Cu(111) surface and see the above
behavior (for both surface and bulk states). I suspect
the oscillation is related to some kind of insufficient
precision but don't know what it is exactly. The calculation
is done with 4000 k points and charge convergence 0.00001.
Can anyone explain or/and resolve this phenomenon?

Thank you
Chiung-Yuan