[gmx-users] Anomaly in Temperature Behavior

[S. Alireza B]

Hi,

We are doing a simulation on a heterogeneous three phase system (gas,
liquid, solid) surrounded by two silica surfaces which are kept frozen.

To set up the simulation at 300 K, we first perform a 0.5 ns NVT simulation
which runs without a problem. During this run we freeze the solid phase in
all three dimensions. We then take the final configuration of this run,
unfreeze the solid phase, and subject it to a long NVE simulation to study
the dissociation of the solid phase (this is similar to melting of ice)
which is an endothermic process.

However, the initial temperature of the NVE simulation is around 185 K
while the end temperature of NVT is ~300K. Also, the temperature keeps
increasing which is contrary to the physical fact that the dissociation
process is endothermic.

(I have run the same system with DL_POLY 2.20 and observed gradual
temperature decrease as the result of solid decomposition.)

I appreciate being advised on what might be wrong with my system?

I am attaching the mdp and topology files for these runs.

-- 
S. Alireza Bagherzadeh
PhD Candidate
Dept. of Chem. & Bio. Eng.
University of BC
2360 East Mall
Vancouver BC V6T1Z3