Why does my volume suddenly expand as I increase temperature.

From: Martin, Erik W (Erik.Martin_at_stjude.org)
Date: Mon Nov 11 2013 - 17:55:05 CST

So, I have set up simulations where every 2 nanoseconds I increase the temperature by ten degrees. The goal of this simulation was to attempt to "melt" structures that had previously formed at constant temperature. It is possible that I went about this in a rather naive way, and would appreciate any insight.

I accomplished this by simply rescaling velocities and resetting Langevin Temp and Piston Temp to the current temperature in a short tcl script. I did not anticipate that the volume would be static in these simulations, but was a bit surprised by what I saw.

The simulation seemed to progress fine with actually very little change in Volume until it got to 550 degrees. At this point I saw a sudden explosion in volume accompanied by a drop to near zero pressure. These jumps appear to also include a sudden increase in total energy. I've never done this sort of thing before and am not sure what I am actually seeing happen.

If anyone can interpret this for me, I'd greatly appreciate it.


PS. This is a simulation in TIP3 water of ~90k atoms.

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