[gmx-users] nve energy conservation

[Jo]

Hello,

I posted earlier regarding running an NVE simulation for a box of 1000 SPCE
water.  I have tried  many different parameters based on other gmx_users
email list questions (changing verlet-buffer-tolerance, timesteps, cutoffs,
coulombtype, vdw-type, etc), but still I am unable to conserve energy. The
energy shift is catastropic (~300 kJ/mol/ns).

Thanks Mark for referring me earlier to the manual with the energy drift
figure!  I think the drift I am experiencing is much more significant than
that depicted in the figure though.

Below are the parameters I am using, I feel like I must be making a major
mistake in my mdp file.  I assume using Potential-shift for coulombic and
vdw will satisfy energy conservation for both energies.  I have not tried
double precision yet but I assume it will not help with the massive energy
shift I am seeing.
Please let me know if anyone has any suggestions on what I can try or
anything I am wrongly assuming!

verlet-buffer-tolerance  = -1
rlist = 1.3
coulombtype = PME
rcoulomb = 1.3
coulomb-modifier = Potential-shift
vdw-type = Cut-off
rvdw = 1.3
vdw-modifier = Potential-shift

Best,

Jo