Phase transition

Dear LAMMPS users ,

Greetings .

I have plenty of molecules (type A) around one special molecule (type B).
I increased the temperature of molecule B exclusively so now some of A molecules that are close to B have different temperature in comparison with A molecules that are far from B.
How can i check the phase transition of A molecules ( closest one to furthest one ) at this system?

I appreciate your opinions in advance.

Best Regards.
Saeed

A phase transition is not a single thing. If you want
to look for a change in the local lattice conformation,
you can try several of the compute */atom commands,
like compute centro/atom, compute cna/atom, compute

coord/atom, etc.

Steve

Hi .

Thank you Steve because of your replay .
Actually I want to know the Phase of A molecules ( closest one to furthest one from Molecule B ) that have different temperature .
Is it possible with using of these " compute" commands ?
I appreciate your opinions in advance.

Regards,
Saeed.

Hi .

Thank you Steve because of your replay .
Actually I want to know the Phase of A molecules ( closest one to furthest
one from Molecule B ) that have different temperature .
Is it possible with using of these " compute" commands ?

this is not something that can be answered with a single yes or no.
phase transitions are a complex process and - more importantly - a
process of a bulk system and not of a single or a few molecules. also,
phase transitions are often a nucleated and thus activated process and
thus subject to finite size effects and dependent on rare events. that
all being said, those computes that steve mentioned can be used to
characterize the local environment of atoms, which is somewhat
indicative of phase transitions. how much for any of those and in
which way, is your job to find out.
in general, it seems to me that you should first spend a little more
time researching how the kind of phase transition you are interested
in has been studied in the past in atomistic simulations and what
parameters of such studies were using as indicators.
and you should keep in mind that LAMMPS is toolbox and not an
artificial intelligence. all it can do is to perform calculations that
you ask for and characterize them; interpreting this data and drawing
conclusions is up to you and therefore requires that you spend some
time understanding what is going on rather than just stuffing some
geometry into the program and waiting for it to spit out the answer
you are looking for right away.

axel.

Hi .

Dear Axel , thanks a lot because of your comprehensive replay .

I just want to know Is it possible for LAMMPS to do some analysis about A molecules Phase that are around B molecule ?

As I told you before I have plenty of molecules (type A) around one special molecule (type B) and I want to check these A molecules Phase after changing the temperature of B molecule .

I appreciate your opinions in advance.

Regards,
Saeed.

I forgot to tell you that I am just looking for a way and actually output that can help me to find out that at a certain distance of B , A molecules will be liquid , gas or …

Thank you again .

I forgot to tell you that I am just looking for a way and actually output
that can help me to find out that at a certain distance of B , A molecules
will be liquid , gas or ...

in order to compute distance dependent properties, you should output
per-atom properties as part of a custom dump file and then
post-process them.

I already told you of compute commands that

can do local structural analyses around each atom.

Your other email said you are looking for a “phase” where

nearby molecules are at a different temperature than
others. That doesn’t make sense to me, b/c the

energy (temperature) will simply re-distribute rapidly
to neighboring atoms/molecules.

Steve

Hi .
Yes Steve that’s right .
Actually I want to increase the central molecules temperature suddenly and at femtosecond I want to check other molecules phase . At this very short time i can say that some molecules that are close to center have high temp than molecules far from that.

Hope to be clear for you .
Thanks for your attention.

Regards,
Saeed.

The compute atom/molecule and compute ke/atom

commands can be used to sum up the kinetic
energy on a per-molecule basis. Which could then
be output be fix ave/time. You’d have to do
some post-analysis to flag what you are calling
“phases” in a spatial sense.

Steve

You may measure rdf to check if a certain type of atom is available around another atom type.