[lammps-users] Rigid body simulation?

Hi all,

I want to simulate potassium carbonate and lithium carbonate.
I used LJ and coulomb interactions and no bond/angle/dihedral/improper.
I want to know how to treat a molecule as a rigid body.
I tried none for all bond/angle/dihedral/improper style and it didn’t work.
I also tried fix/rigid, fix/poems, and fix/shake command and none of them worked.
What happened is that my simulation box has 300 carbonates and the fix/rigid command treats all carbonates as one rigid body.

Anyone knows how to solve this problem?

Thanks,

Dong

Hi all,

hi dong,

I want to simulate potassium carbonate and lithium carbonate.
I used LJ and coulomb interactions and no
bond/angle/dihedral/improper.
I want to know how to treat a molecule as a rigid body.
I tried none for all bond/angle/dihedral/improper style and it didn't
work.

"don't work" is a very strong statement. if those components
of LAMMPS would not work, how come that so many people can
use them successfully. so it is more likely, you don't understand
how to write a proper input for your system.

I also tried fix/rigid, fix/poems, and fix/shake command and none of
them worked.

What happened is that my simulation box has 300 carbonates and the
fix/rigid command treats all carbonates as one rigid body.

you obviously didn't read the documentation of fix rigid
well enough. check out the "bodystyle" option.

however, for a system like you describe it, i'd rather
try fix shake first, as it should allow you to use a
much larger time step. remember that for fix shake the
constraint distance/angle is taken from bond/angle_coeff
definitions, so you have to define them, even if only
with a dummy force constant, e.g. 0.0.

Anyone knows how to solve this problem?

you have to read the documentation more carefully.
all you need to know is in there.

cheers,
   axel.