tip3p water_NPT

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1

Hi,

I got some trouble in equilibrating my water + NaCl solution.

I want to get the equilibrium cell size at room temperature and room pressure, so I launch NPT runs. But, the simulations always crashed with missing bond atoms or missing shake atoms, while no error when using NVT. So what should I do? if I could run NPT, how to get equilibrium cell size?

Any suggestions or comments? (input file is shown below)

Thanks,

2

What is the system pressure relative to your target pressure? What is the simulation box doing when you invoke fix npt?

Monitor it every timestep. If they dynamics are bad, then you have to fix it.

You could adjust the barostat relaxation time for example.

Steve

3

Hi, Steve

the system pressure fluctuates violently at the scale of ~ 400 bars around my target pressure 1 bar. is the results still reliable with so large fluctuation?

If I increase the barostat relaxation time, the simulations would just crash at later time.

If I have to fix it, then I just don’t know which cell size to fix it to.

Thanks,

Cunzhi

4

I don’t know. If your time constant is big enough, there is
no reason the volume should change rapidly. If it doesn’t
then there is no reason you should lose atoms in well-behaved
dynamics. If your system is large enough there should not
be huge abnormal fluctuations in pressure (though pressure
does fluctuate, esp for solids).

Steve