Prevent MM water diffusion into QM box.

[ilya]

Hello!

I am doing a QM/MM calculation -- a small molecule and some QM waters
in a large MM water box (periodic).
After a while the calculation stopped saying that geometry is broken.
I noticed that most of QM waters are near the borders of the QM cell
(the walls are on) and they are substituted by some MM ones (so there
are some artifacts in the geometry, that's why I think calculation
stopped).
There is a section CP2K_INPUT / FORCE_EVAL / QMMM / WALLS to prevent
QM waters float out of the box.
Is it possible to prevent MM waters float into the QM box, because it
seems that diffusion is unavoidable regardless of water density in the
QM box.

Thanks a lot.
Ilya.