[gmx-users] NVE simulations
lindahl at stanford.edu
Fri Jul 12 22:16:00 CEST 2002
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.
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.
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