[lammps-users] How angles are handled?

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1

Dear Lammps users and developers,

I’m a rookie trying to understand how Lammps handles the three-body interactions for ionic materials (no molecules). I found a data file containing all atom, bonds and angle info in the examples\USER\cg-cmm, so does it mean the anglelist is pre-determined as input and will not change throughout the simulations, and the three-body calculations will only be carried out among those triplets specified in the Angles section in the input file? If this is true, is it generally true for all three-body potentials (cosine-squared, SW, Tersoff…) that the anglelist is pre-determined and will not be dynamically updated throughout the simulations? If this is not true, could you please let me know how three-body interactions for ionic materials are handled in Lammps? Thanks a lot!

2

Dear Dr. Plimpton,

Could you please help me with that? Thanks!

Bo

3

dear bo,

you should start by reading a text book about molecular
simulations and force field definitions.

there is a _big_ difference between manybody potentials
and force fields with a mix of bonded (bonds, angles, dihedrals)
and non-bonded interactions (lj and charges). the USER-CG-CMM
examples actually _not_ all atom simulations but a coarse grain
model.

cheers,
   axel.

4

Any interaction compute with an angle style uses
a fixed list of 3-body interactions. Any many-body interaction
computed with a pair style does not. Rather it infers
the set of 3-body interactions dynamically from the current
config of all the atoms. No list of angles is provided
or stored.

Steve