some basic questions

Dear LAMMPS users,

I am new to LAMMPS and have several basic questions. I have read the manual and do not understand the questions clearly yet.

  1. What are ghost atoms?
  2. How is the interaction between two particles(atoms) represented in LAMMPS, using a force vector or a stress tensor?
  3. How does the command ‘MPI_Allreduce’ work?
  4. What is virial? Is virial the stress at a particle(atom)?

These questions may seem to be too basic for you guys (yet very difficult for me). I hope I do not bother you too much…

Thanks for your time and help!

Best regards,

Tom Smith

Dear LAMMPS users,

I am new to LAMMPS and have several basic questions. I have read the manual
and do not understand the questions clearly yet.

please note, that the manual is no replacement
for leaning/understanding principle of MD simulations.
the manual explains how to *use* LAMMPS. it is
*not* a document that will teach you how to do
MD in general and correctly.

1) What are ghost atoms?

those are atoms that are "owned" by neighboring domains.

2) How is the interaction between two particles(atoms) represented in
LAMMPS, using a force vector or a stress tensor?

this is not a very precise question. the interaction between
atoms is represented by their interaction potential, which
may consist of multiple terms. those are implemented in
LAMMPS as "styles" which then compute their contribution
to forces and, if needed, potential energy and stress.

3) How does the command 'MPI_Allreduce' work?

this is part of the MPI standard for message
passing and thus far beyond the scope of this
mailing list. please use a search engine. there
is a gazillion of material on MPI online.

4) What is virial? Is virial the stress at a particle(atom)?

http://en.wikipedia.org/wiki/Virial_stress
http://en.wikipedia.org/wiki/Virial_theorem

These questions may seem to be too basic for you guys (yet very difficult
for me). I hope I do not bother you too much..

they mainly demonstrate that you are
looking for help in the wrong place and
that you need to learn some more basics
before you should be doing anything
with LAMMPS. please have a look at:

http://lammps.sandia.gov/guidelines.html

axel.