Dear lammps-users,
I am running a stretching simulation for a 1000 atoms crystalline silicon model, with boundary condition ppp and Stillinger-Weber potential . The model box is 27.15355^3 Angstroms^3, and I checked that there is no overlapping atoms. I used a “fix nve” and "fix temp/rescale " command to heat up the model from 0 to 300k, but after heating up, the pressure went to 4000 bar, which was too high. If I use “fix npt” instead of “fix nve” to release the pressure, the box will become too large and explode due to the high pressure when heating up.
I tried to change a potential such as Tersoff, the pressure became -2000, still abnormal. Besides, I tried a spp boundary (my load is in x direction), but it did not work.
Do you know what’s wrong?
Thanks!!
Kay
Dear lammps-users,
I am running a stretching simulation for a 1000 atoms crystalline
silicon model, with boundary condition ppp and Stillinger-Weber potential .
The model box is 27.15355^3 Angstroms^3, and I checked that there is no
overlapping atoms. I used a "fix nve" and "fix temp/rescale " command to
heat up the model from 0 to 300k, but after heating up, the pressure went
to 4000 bar, which was too high. If I use "fix npt" instead of "fix nve" to
release the pressure, the box will become too large and explode due to the
high pressure when heating up.
I tried to change a potential such as Tersoff, the pressure became
-2000, still abnormal. Besides, I tried a spp boundary (my load is in x
direction), but it did not work.
Do you know what's wrong?
how should anybody know? most likely because parts of your input deck is
messed up. there are more things that can go wrong than just overlapping
atoms. popular mistakes are wrong choice of units or too large a time step.
one general thing about pressure in small fairly incompressible systems
(1000 atoms is *very* small): since very small displacements can cause
large forces and thus large pressure values, you have to make sure that
your lattice constant is correct. but here you need to use the lattice
constant of the respective potential and not the experimental value. those
often differ enough to cause significant changes in stress.
axel.
axel.