How to convert simulation box type

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#1

Dear LAMMPS users,

Hi,

Currently I’m working on a simulation and My initial simulation box is triclinic. However, I have to make a cubic one for some mechanical simulation. So, any help on how to make a cubic simulation box fast and easy ?!

Thanks in advance,

Ali

#2

Hi,

I am not sure about what you want to do but you may want to have a look at the following link:
http://lammps.sandia.gov/doc/change_box.html

Thanks,
Sara

#3

Hi,

I am not sure about what you want to do but you may want to have a look at
the following link:
http://lammps.sandia.gov/doc/change_box.html

Thanks,
Sara

Good link! One minor warning: the "change_box" command will
instantaneously change the boundary conditions of your simulation.
This might cause atoms to overlap. If that happens, your the forces
between particles will be huge and your simulation will probably
crash, especially if you don't minimize the system first. For
details, see:
http://lammps.sandia.gov/doc/minimize.html

To avoid this problem, you can deform the box shape gradually from a
triclinic to a rectangular shape. For more details check out:
http://lammps.sandia.gov/doc/fix_deform.html

I'm not sure if this answered your question.

If instead you are just generally curious how to build a system with
rectangular boundary conditions, then feel free to read my answer to
the other message that you posted a few days ago.

cheers

andrew

(probably not a good idea to post multiple copies of the same question
to the list)

#4

Dear Sara and Andrew,

I really appreciate your responses. About the ambiguity of my question, Actually I have a structure with monoclinic lattice structure ( So my .cif file is monoclinic ). For the sake of simulation, I need to have a cubic simulation box. But if I use that .cif file obviously it is not cubic. By the way, my apology to send the question several time. I wasn’t familiar of how this community works.

Sincerely,

Ali

#5

Dear Sara and Andrew,

I really appreciate your responses. About the ambiguity of my question,

ambiguous is a rather euphemistic attribute.

Actually I have a structure with monoclinic lattice structure ( So my .cif
file is monoclinic ). For the sake of simulation, I need to have a cubic
simulation box. But if I use that .cif file obviously it is not cubic. By

create your proper monoclinic geometry cell from the cif file. be
careful to expand all symmetries, remove redundant positions and note
fractional occupations, if they exist.

from that you can create a supercell. how many times you need to
replicate in the direction of the tilted axis depends on the amount of
tilt. it has to add up to approximately the length of one unit cell in
x direction, so that you can reset the box to be cubic and still have
a correct periodic boundary.

the way, my apology to send the question several time. I wasn't familiar of
how this community works.

please see:
http://lammps.sandia.gov/mail.html

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

and use common sense.

axel