Output the simulation box volume and npt

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1

Dear all,

I’m trying to simulate the nucleation of a Si nanoparticle. Before doing that, I want to see the phase-transition temperature for bulk Si.

So I simulate a cubic 5X5X5 cell in PBC, using npt.

I want to locate the jump in potential energy or volume, to indicate this transition; however, it seems that the simulation box volume is not in the c_thermo_vol or npt fix. Does anyone know how to access that value?

Also, I’m not quite sure about the use of npt, as the pressure during simulation is way higher than the 1.013 I specified. Could anyone help me explain how to use npt to implement the melt-quench method in LAMMPS?

Units metal

Timestep 0.0005

fix 1 all npt temp 3000.0 3000.0 0.5 iso 1.013 1.013 0.5 drag 0.3

Thanks,

Andy

2

You can output the box volume with the thermo_style command.
What is the "multi-quench" method?

Steve

3

Sorry. I'm meaning melt-quench approach.

I wanted to use nvt to melt a Si nanoparticle (suspended in vacuum), and
equilibrate it, and quench it down. To locate the phase transition T, I
tried to melt bulk Si first using npt, equilibrate, and quench.
The code for bulk Si looks sth like

Units metal
Fix 1 all npt temp 3000.0 3000.0 5.0 iso 1.0 1.0 0.5 drag 0.3
run
Unfix 1
Fix 2 all nve
Run
Unfix 2
Fix 3 all npt temp 3000.0 1000.0 50.0 iso 1.0 1.0 0.5 drag 0.3
Run

Did I implement it right? The preliminary results I got have large
fluctuation in pressure, and I couldn't see a jump in E(T) plot.

Thanks,
Andy

Andy

4

That's the right idea, but there are lots of ways
to have problems trying to locate a phase transition.
Too much noise, quenching too fast, too small a system,
overshooting due to supercooling, etc.

Steve