Hi Chris,
I experienced the same kind of thing. In the process of building a box
of liquid (organic solvent), at some point I wanted to get rid of a
layer of vacuum around my system. So for shrinking the box I used
similar settings as you and found also that the collapse was going
slower than I'd have expected.
One solution to accelerate this (if your goal is to shrink the box) is
to increase the pressure (to say 100 atm). But it's important to stop
the simulation in time (i.e. once the layer of vacuum has disapeared)
otherwise the system shrinks too much and density is off.
So to come back to your system which has a very big layer of vacuum
around, and according to my experience, the volume is probably
decreasing but too slowly to see anything signigicant (compared to the
initial value) in 200 ps .
Ciao,
Patrick
Le 21/03/2011 16:53, chris.ne...@utoronto.ca a écrit :
Dear users:
I recently came across a system that was composed of tip4p water vapor
droplets separated by vacuum. This system is what you might get if you
did a NVT simulation of water with a box that was 10 times too large for
the number of water molecules.
I was surprised to see that this system did not collapse to any
significant extent during 200 ps of NPT equilibration at 1 atm using the
Berendsen thermostat with tau_p=1.0 and the sd integrator and a colombic
cut-off. (We also tried a number of other integrator/pressure coupling
combinations with the same results).
I had assumed that such collapse would occur quite rapidly. This does
not seem to be the case (no noticeable contraction within 200 ps).
Has anybody else done anything like this? Can anybody comment on their
expectations/experience of collapse from the gas state to the liquid
state under standard NPT conditions?
Thank you,
Chris.
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Patrick FUCHS
Dynamique des Structures et Interactions des Macromolécules Biologiques
INTS, INSERM UMR-S665, Université Paris Diderot,
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Web Site: http://www.dsimb.inserm.fr/~fuchs
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