Hi every one
I want to apply a uniform compression on a bar made of Ferrite with dimensions 10nm100nm10nm along x, y and, z directions. I have used f p f (free periodic free) boundary conditions. My goal is to make the Ferrite yield when the loading is in the y direction.
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my first question is that is my boundary condition reasonable (f p f)?
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when I use free boundary condition I get an error: Cannot use fix npt for non-periodic boundary conditions. How can I get rid of that?
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When I use fs boundary condition instead of f, it gives me another error: Lost atoms
------------------------ INITIALIZATION ----------------------------
units metal
dimension 3
boundary f p f
atom_style atomic
neigh_modify delay 5
----------------------- ATOM DEFINITION ----------------------------
lattice bcc 2.8553
region box block 0 35 0 350 0 35
create_box 1 box
lattice bcc 2.8553 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
create_atoms 1 region box
------------------------ FORCE FIELDS ------------------------------
pair_style eam/fs
pair_coeff * * Fe_mm.eam.fs Fe
------------------------- SETTINGS ---------------------------------
compute csym all centro/atom bcc
compute peratom all pe/atom
Hi every one
I want to apply a uniform compression on a bar made of Ferrite with
dimensions 10nm*100nm*10nm along x, y and, z directions. I have used f p f
(free periodic free) boundary conditions. My goal is to make the Ferrite
yield when the loading is in the y direction.
1) my first question is that is my boundary condition reasonable (f p f)?
not really. you may use fixed boundaries, but you need to leave extra
space. it'll be easier to use shrinkwrap, though.
2) when I use free boundary condition I get an error: Cannot use fix npt for
non-periodic boundary conditions. How can I get rid of that?
either by not using a variable cell integrator (not much sense to it
for your setup anyway), or by coupling only the periodic box dimension
to the npt integrator. please see the documentation.
3) When I use fs boundary condition instead of f, it gives me another error:
Lost atoms
no surprise there. you have no space between your fixed boundary and
your atoms, so even from lattice vibrations they'll "fall out of the
box".
BTW: your later input is incorrect as well. there is no sense at all
in running fix npt and fix deform at the same time. you'll have two
fixes "fighting" over changing the box. this will lead to bogus
results at best, and crashes more likely.
axel.
These question lie outside the scope of the LAMMPS mailing list. People have been doing simulations of this type for several decades and publishing their findings. It behooves you to read the fruits of their labors, instead of looking for a quick fix. Once you have figured out the best way to run your simulation, you can start to ask LAMMPS-specific questions like “How do I apply external forces to two chunks of atoms on opposite ends of a nanorod?”
Aidan