[gmx-users] size of the system

[V.V. Chaban]

Dear Colleagues,

I've got a novice question as for GROMACS. For example, I need a system
of 500 water molecules. Initially, I've spc216.pdb. Then I try:
pdb2gmx -f spc216.pdb -o conf.pdb
editconf -f conf.pdb -o box.pdb -d 0.7
genbox -cp box.pdb -cs spc216 -o water.pdb -p topol.top
The utility outputs:
"......
solvent configuration contains 648 atoms in..."

and hangs up.

Where am I wrong? And how can one obtain the system of the desires
quantity of molecules using GROMACS utilities?

Thanks in advance.

-- 
Vitaly