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

[Jochen Hub]

csreddy at ncbs.res.in wrote:
> 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
>   
Theres is something wrong in your calculation of the density. From 32885 
Molcules (18g/mol) in a volume (10nm)^3 I get a density of 982 g/l.

Cheers, Jochen
>
> 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
>
>
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-- 
************************************************
Jochen Hub
Max Planck Institute for Biophysical Chemistry
Computational biomolecular dynamics group
Am Fassberg 11
D-37077 Goettingen, Germany
Email: jhub[at]gwdg.de
************************************************