[Pw_forum] !Charge density of "Sadam Hussein"

[Noah_Park]

Dear All;
When I calculate Iron atoms in the interstitial of graphite,
I found the following messages are persistent over the self-consistency steps.
   > npt with |zeta| > 1 : 53321, npt tot 878400, 6.10 %
   > npt with rhoup <0 : 266028, npt tot 878400, 30.41%
   > npt with rhodw<0 : 266028, npt tot 878400, 27.81%

Assuming it is due to incompleteness of FFT mesh, I increased the energy cutoff.
But such "npt"s do not decrease measurably.
My question is that,
    1. what is the origin for such unphysical(?) charge density on a certain point ?
    2. Is it really no problem, as the code does not produce warning message ?

When I tested Iron bulk(FCC, and BCC), very small amount of  such npt points appear,
    > npt with rhoup <0 : 1, npt tot 5832, 0.02%.
However, appearing physical results, for example, 
the energy difference between nonmagnetic FCC and magnetic BCC looks decent.

I really appreciate any of comments.

Noah