[gmx-users] NVE simulations

[Erik Lindahl]

Sidney Elmer wrote:
> I've never used SPC water, so I may be wrong here, but I can take what I learned from CCL4
> and hopefully it will apply to spc water as well.  I would guess that you are really running
> with constraints, even when you think you aren't.  In the spc.itp file, the section "settles"
> imposes constraints on the water molecules, even if you set the keyword "constraints"
> argument to "none" in the .mdp file.  The same thing happened to me with CCL4, where
> I defined constraints in the topology file.  You should try using flexspc.itp instead, which
> defines bond and angle parameters, and has no constraints built into the topology.  My guess
> is that the total energy will remain constant in this case, as long as you set the
> "constraints = none" keyword in your .mdp file.  If that doesn't work then I am just as
> befuddled about NVE simulations as you.  Good luck.
> 
> Sid

Hi,

You could also increase the parameter lincs_order to 8 in the mdp file - 
this will make the restraints more accurate which might be necessary in NVE.

Cheers,

Erik