[gmx-users] temperature control

[B. Nick]

Dear all,

I want to run a MD simulation of a 74 atoms
solute in 1600 SPC water molecules at 371 K.
I coupled each group (solute and solvent)
separately to the temperature control. 
If I analyze the temperature after MD
I see that the solute is about 370 K whereas
the water cools down to 251 K during the
first ps of the run. This happens
irrespectively of the thermostat and timestep.
I used Berendsen and Nose-Hoover with a timestep
of 1fs or 0.5 fs.
Why isn't the temperature of both near 371 K?
Can anyone explain this to me?

Thanks in advance,
Gitta

-- 
Dr. Birgitta Nick
Deutsches Wollforschungsinstitut
Veltmanplatz 8, D-52062 Aachen, Germany