[gmx-users] Concentration of Urea in urea solvation box

[mon_sharma at research.iiit.ac.in]

Hi All,
This is a trivial question. But I am quite puzzled about it, and I 
really need someone's kind help.

I want to prepare 8M urea solution box, 
for which I might need to know input as number of water molecules and of 
urea. Now my query is how to make sure of these exact number of molecules. 
I know its really a basic question. One thing could be by experiment if we can make sure exact 
number of moles of water added to make molar solution. But i dont have any 
access to such wet lab things. So if anyone can help me out how to do 
these back end calculations.
Another query is will the box size also play a role?

Please be patient with this trivial query, but this simple 
calculation question is baffling me from quite a few days.

Thanks in advance,
Regards,
Monika