[Wien] vacuum space in slab calculation

[Griselda Garcia]

Hello!! Wien Users

I am trying to do Si(001) slab calculation using a slab with 11 layers 
and a vacuum of  10, 15 and 20 angstrom and the potential at the center 
of the vacumm is still to large.

10 A   ->  :VZERO:v0,v0c,v0x  -1.25711  -0.60101  -0.65610 v5,v5c,v5x   
0.33972   0.35066  -0.01093
15 A   ->  :VZERO:v0,v0c,v0x  -1.10002  -0.44415  -0.65587 v5,v5c,v5x   
0.48087   0.50787  -0.02700
20 A   ->  :VZERO:v0,v0c,v0x  -1.19412  -0.53647  -0.65766 v5,v5c,v5x   
0.40499   0.41492  -0.00993

Should I still increase the vacuum in the cell? is it normal such a 
large value?
Could exist any other problem?

Thank you!! for your time and advise.

Griselda
Pontificia Universidad Catolica
Chile