[lammps-users] Temperature going down to zero!

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1

Hi Sourav,
I have a few questions.

  1. Does temperature remain constant for a long period of time without the introduction of new silver atoms?
  2. What happens to the potential energy?

Regards,
Rutuparna

2

Rituparna and everyone,

Here are my observations:

The temperature and potential energy remain pretty constant (even over long
time) if the singular silver atom is not introduced. Even after the
introduction of the silver atom, the temperature and also the potential energy
remain constant till this silver atom reaches near the surface of the core,
gets pulled toward it and hits the surface of the crystal (Ag core). When it
hits the surface the temp jumps up and gradually and steadily falls as the
silver atom keeps on colliding with the silver atoms at the surface of the
crystal. At the same instant, the potential energy falls steep first and then
gradually and steadly (attached a picture).

Hope I have given a better insight now.

Looking forward to your suggestions.

Thanks very much.
Sourav

Hi Sourav,
I have a few questions.
1. Does temperature remain constant for a long period of time without the

introduction of new silver atoms?

2. What happens to the potential energy?

Regards,
Rutuparna

________________________________

From: [email protected] on behalf of Sourav Ghosh
Sent: Thu 8/23/2007 8:55 AM
To: Steve Plimpton
Cc: [email protected]
Subject: Re: [lammps-users] Temperature going down to zero!

Steve and all group members,

Thanks for your suggestion. I ran another simulation. In this one, the core

is

silver (441 atoms) and 10 singular silver adatoms are introduced one after
another at a gap of 1000 picoseconds. It is evident from the attached picture
that the temperature sharply goes up everytime when a new adatom (in this

case

silver) is introduced and then steadily goes down. The total energy is also
dropping slowly. I have not changed the previous code other than

incorporating

9 more silver adatoms and changing the delay between each.

I am still pondering over why this could happen. Any help would be vital for
my work and much appreciated.

Thanks,
Sourav

In message
<[email protected]...> "Steve

Plimpton"

<[email protected]> writes:
> I don't see anything obvious wrong. You might try removing the angular
> momentum fix - I doubt it is doing much. You can zero the angmom
> when velocities are created. I would run a smaller, shorter simulation
> to debug it.
>
> Steve
>
> > Hi,
> >
> > I have now upgraded the LAMMPS version and got rid of the 'illegal
> > create_atoms command' error. Valeria was right to point that out. Thanks

to

> > everyone for your suggestions. Now I having a major problem, which I

can't

> > make out why. It would be great if you could throw some light on this.
> >
> > The Ag core of 441 atoms (radius 3 lattice units) equilibrated quickly.

But

> > then when I introduced single silver atom at radius 6 lattice units and
gave
> > it a small velocity toward the core, the temperature (and thus kinetic
energy)
> > started going down rapidly when the single Ag atom came closer to the
surface
> > of the core and entered its subsurface. The temperature went to zero when
run
> > for longer time. There is just the Ag core and one Ag atom approaching

it,

PE_26.jpg