[gmx-users] Simulations in extreme conditions

[Dr. Vitaly Chaban]

I like extreme conditions... Seriously.

OPLS water, as well as other popular MM waters, are parametrized for
liquid state. I think you need to decrease model's dipole moment and
you have to work with an integration time-step to ensure adequate
energy conservation at ca. 600K.

I believe there should be exotic water models that were trained to
reproduce the phase diagram to certain extent.

Vitaly



On Fri, Feb 14, 2014 at 7:58 PM, CipPruteanu <C.Pruteanu at ed.ac.uk> wrote:
> Hi everyone!
>
> I am trying to run a simulation of methane-water mixtures under extreme
> conditions, that is around 25 kbars and 600K (and maybe higher in both
> pressure and temperature).
>
> I am currently using OPLS for methane with TIP3P for water. The way I
> proceed is as follows:
>
> -generate a box of methane and water having my desired concentration
> -do an energy minimization for 100ps
> -do a NVT equilibration at my desired temperature for 100ps
> -do a NPT equilibration at my desired pressure and temperature for 100ps
>
> -run the simulation (NPT) for as long as I desire (1-10 ns for the moment)
>
> The simulations I ran on the individual components get reasonably good
> results for them under these conditions. However, once I put them together,
> the mixture doesn't behave as expected (by recent experimental findings).
>
> Is this approach ok or is there something fundamentally flawed about it ? I
> know the fact that the forcefields are not meant to be used at these high
> pressures/temperatures, but apart from that, is there anything I could
> improve?
>
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