# apply electric field on ellipsoids(without charge)

Dear users,

I am a new lammps user and I want to know if there is any way to apply electric field on the particles with gayberne pair-style. I am assuming particles don’t have any charge and the applied electric field induces dipole-moment to the ellipsoids.

Regards

Dear users,

I am a new lammps user and I want to know if there is any way to apply
electric field on the particles with gayberne pair-style. I am assuming
particles don't have any charge and the applied electric field induces
dipole-moment to the ellipsoids.

​i am not aware of an existing feature, that can do this.
thus in order to realize such a model, you would have to program your own
custom fix style to apply the required force/torque to the particles.

axel​

You can assign point dipoles to spheroids or ellipsoidal particles. See

the atom_style dipole command. Then you could use pair hybrid

to use (a) pair gayberne for the LJ-like ellipsoidal interactions,

and (b) pair lj/cut/dipole/cut to do the dipole/dipole interactions,

with the LJ terms in that potential set to epsilon=0.0. Or dipole/long

with ewald.

We should probably add a simple pair dipole/cut and dipole/long

to make this easier to add dipole interactions to any potential.

Looks like we also need to add a “dipole” keyword to fix nve/asphere

(like for fix nve/sphere) to update the dipole direction when the

ellipsoid rotates.

Steve

You can assign point dipoles to spheroids or ellipsoidal particles. See
the atom_style dipole command. Then you could use pair hybrid
to use (a) pair gayberne for the LJ-like ellipsoidal interactions,
and (b) pair lj/cut/dipole/cut to do the dipole/dipole interactions,
with the LJ terms in that potential set to epsilon=0.0. Or dipole/long
with ewald.

that would still require to write a fix to compute/update the dipole
according to a polarizability tensor as indicated in the original post.​

​axel​

the applied electric field induces dipole-moment to the ellipsoids.

I assumed this comment in the original post meant the user

would assign a fixed magnitude dipole moment to the particles

and wants the applied E-field to interact with it. LIke a Stockmeyer

model, but for ellipsoids.

It instead, as Axel indicates, you want some form of a true polarizable potential,

then LAMMPS does not have those, even for spherical paritlces,

other than what is part of the COMB potentials.

Steve

pair lj/cut/dipole/cut can be used if i have predefined fixed dipole moment values of particles, but here I want electric field to couple with long axis of the ellipsoid and update the dipole moment accordingly at every step as Axel has indicated in his reply.

If you want fix efield to interact with individual dipole moments and adjust their length,

then writing a derived class from fix efield that includes this effect is easy to do.

That is, if the comptuation involves the Efield and a single dipole and it changes

the length of the dipole (or also induces a torque, which is what fix efield currently does).

If the calculation is a collective effect involving many dipole moments, then that’s

more like a polarizable force field and would need to be implemented as a pair style.

Steve