system with atom or granular clusters

Hello all,

I am trying to construct a system where set of atoms or granules are glued together as clusters with attractive forces between them. All such clusters are placed in a box and external forces are applied. These clusters should break into group of atoms/granules when external forces overcome the attractions between them. Which atom-style or fix options are used to construct this system?

I tried using atom-style body and created clusters of atoms. It says in the documentation page (http://lammps.sandia.gov/doc/body.html) that these body particles(collection of atoms) are deformable. But when I apply external forces, these clusters do not break. How can we deform these body particles? What fix command is required to deform these clusters in atom_style body?

Thanks,
Vahini Reddy

Hello all,

I am trying to construct a system where set of atoms or granules are
glued together as clusters with attractive forces between them. All such
clusters are placed in a box and external forces are applied. These
clusters should break into group of atoms/granules when external forces
overcome the attractions between them. Which atom-style or fix options
are used to construct this system?

that depends on the functional form that best describes those
interactions. from the information you provide, a simple system with
atom style atomic and pair style lj/cut or morse might work. for more
irregular potential shapes, you could also use pair style table.

I tried using atom-style body and created clusters of atoms. It says in
the documentation page (LAMMPS Molecular Dynamics Simulator) that
these body particles(collection of atoms) are deformable. But when I

no, it doesn't. it says, that they *can* be deformable, but if you
read on carefully, you'll discover, that you would need to program a
suitable integrator for that and that for now only a rigid body
integrator is provided as an example for such an integrator. at any
rate, those bodies are not designed to break apart and thus this is
not suitable for your simulations.

axel.

As an add on (most appropriate for clusters of granules), you can easily construct clusters of particles/granules with any additional attractive potential (short or long ranged) that you like and the standard granular models. I give a list of papers below (some are my own) if you’re interested in some example models.

But even then, these clusters bound by interparticle forces generally cannot break-up due to external forces - unless there is a substantial force gradient at the scale of the cluster of particles. Because in classical mechanics there needs to be a relative force between particles to separate them. Even in the case of hydrodynamic drag being the external force resolved by solving fluid equations with appropriate boundary conditions, unless the drag on one particle in the cluster is substantially different from that of neighboring particles, you’re not going to see break-up. For athermal assemblies (no substantial Brownian effects) break-up is typically caused by collisions and thus the related velocity fluctuations/impact velocities.

You may want to reconsider your set-up, if an external force is what you’ve been considering.

HTH in some way.

Brewster et al. (2005) Phys Rev E (http://journals.aps.org/pre/abstract/10.1103/PhysRevE.72.061301) (Short-ranged Gaussian potential)
Mueller & Luding (2011) Math. Modell. Nat. Phenom. (http://www.mmnp-journal.org/articles/mmnp/abs/2011/04/mmnp201164p118/mmnp201164p118.html) (long-ranged potential)
Takada et al. (2014) Phys Rev E (http://journals.aps.org/pre/abstract/10.1103/PhysRevE.90.062207) (Additional LJ potential)
Mehrabadi et al. (2016) Chemical Engineering Science (http://www.sciencedirect.com/science/article/pii/S0009250916303025)
Murphy and Subramaniam (2015) Physics of Fluids (http://aip.scitation.org/doi/abs/10.1063/1.4916674); (2017) Powder Technology(http://www.sciencedirect.com/science/article/pii/S0032591016305769) (DMT colloidal potential for micron-sized contacts)
Kobayashi et al. (2013) Powder Tech. (http://www.sciencedirect.com/science/article/pii/S0032591013001368) (ramp potential - constant force in contact)