<br>
<div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">3000ps is an extremely large coupling constant to want to use.<br><br>In any case, "Simple" is wrong about the frequency of coupling. This
<br>coupling constant is a parameter in an algorithm that is applied each<br>step that expresses how well-connected the group is to the thermal<br>reservoir. It is not a time interval between applications of the algorithm.
<br><br>I suggest you both have a read of section 3.4.5 of the gromacs manual,<br>where it will tell you that "The Berendsen algorithm is stable up to<br>Delta T approx tau_t". Doubtless 3000ps is much larger than your
<br>simulation timestep, and the instability is not surprising!<br><br>Mark<br></blockquote></div>Thanks
for your kind response, but I do not quite agree with your point. I
have used tau_t up to 2ps in my other simulations, and they works fine.
In fact, from version 3.1, it is allowed to not couple certain groups.
I tried that too, and the temperature of water still rises like crazy.<br>
<br>
The manual say that the algorithm is stable upto \DeltaT = tau_t, and I
intepret that as "we can use tau_t as small as \Delta_t", i.e., it
actually pose a lower limit for the coupling constant, rather than an
upper limit. Correct if I am wrong.<br>
<br>
Nick<br>