[gmx-users] Density Deferences between spc216 and tip4p water models

[csreddy at ncbs.res.in]

Dear All,
I was trying  create a  box (cubic 10 10 10) of water. I am a bit
surprised by looking at the density deferences between spc216 and tip4p
water models. I am giving the brief output below.

genbox -cs tip4p.gro -box 10 10 10

Output configuration contains 131540 atoms in 32885 residues
Volume                 :        1000 (nm^3)
Density                :     1639.65 (g/l)
Number of SOL molecules:  32885


genbox -cs spc2i6.gro -box 10 10 10

Output configuration contains 99678 atoms in 33226 residues
Volume                 :        1000 (nm^3)
Density                :     993.966 (g/l)
Number of SOL molecules:  33226

What would be the reason for this drastic differences in density? How can
I make it into 1000 (g/l) by using above command.

Thanks in advance.
Regards
Chandu