# Quenching in a confined volume

Hi LAMMPS users,

I am currently trying to run a quenching simulation on a cylindrical nanowire. The idea is that I want the cylindrical nanowire to have certain dimensions after the simulation. Similar to what happens in metal casting, where the sample is confined to the volume of a mould and you end up with a desired shape at the end.

When I run a quenching simulation in MD this normally doesn’t happen, as the atoms start jiggling around when it reaches the melting point, therefore the shape of the sample ends up being distorted and quite unpredictable.

My approach is as follows but if you could advice of any better way of doing it I would greatly appreciate it.

I was thinking of building a nanowire with the atoms in the surface fixed (by assigning a velocity of 0 to those atoms). I then use fix npt time integration on the rest of the atoms (excluding the surface) to raise the temperature of the sample to 2000K and then quench to 300K.

I have attached the script to have a look.

Many thanks,

Fabian

script1.in (1.85 KB)

Hi LAMMPS users,

I am currently trying to run a quenching simulation on a cylindrical
nanowire. The idea is that I want the cylindrical nanowire to have certain
dimensions after the simulation. Similar to what happens in metal casting,
where the sample is confined to the volume of a mould and you end up with a
desired shape at the end.

When I run a quenching simulation in MD this normally doesn't happen, as
the atoms start jiggling around when it reaches the melting point,
therefore the shape of the sample ends up being distorted and quite
unpredictable.

My approach is as follows but if you could advice of any better way of
doing it I would greatly appreciate it.

I was thinking of building a nanowire with the atoms in the surface fixed
(by assigning a velocity of 0 to those atoms). I then use fix npt time
integration on the rest of the atoms (excluding the surface) to raise the
temperature of the sample to 2000K and then quench to 300K.

​why not simply put a "mould" around your system using fix wall//region
with ​a cylindrical region. no need to use fix npt on that one either,
since you know up front the volume you want to have. when heating/quenching
a system fix npt is not a good idea in the first place. it is easy for a
system to expand and disassemble, but it takes, much more time to shrink
and reassemble.

axel.

I see, I’ll try that approach. Thank you very much for your help!

Fabian