# Some problems about Gay-Berne chain model

Dear LAMMPS users

Hi, there, recently I was doing the research about the GB-chain model. I connect the GB particles to form a polymer chain, however, the orientation of them was chaos in each particle, I tried to control their long axes along the chain direction, but it seems impossible by existing LAMMPS function.

Some functions in LAMMPS I tried are:

1. angle_dipole, it can control the vector angles between dipolar particles, maybe it can control the orientation of GB particles, but it works only for dipolar atoms.

2. asphere_line, it contains the end point to connect bodies, but it works only in 2D system. Maybe it’s possible to connect the end points of two GB particles phsically.

The ways above seems not ideal for the GB polymer chain model.

My problem is that:

1. Though the potential is assigned to a point in the space, can LAMMPS connect GB-particles with their end-point physically?

2. Is that possible to assign GB potential to a 2-point system (like a line segment), which the ellipsoid shape rotates coherently with the chain direction?

Any help would be very appreciated!

Po

1. Though the potential is assigned to a point in the space, can LAMMPS connect GB-particles with their end-point physically?

2. Is that possible to assign GB potential to a 2-point system (like a line segment), which the ellipsoid shape rotates coherently with the chain direction?

Neither of these is possible without writing some code.

What you are really asking for is a bond between 2 ellipsoidal
particles that somehow connects them at their 2 end points

of the long axis of the ellipsoid. That point isn’t even well
defined as the ellipsoids rotate.

What you could try is to represent each ellipsoid
as 3 particles in a rigid body. The ellipsoid and 2 point
particles at either end. The point particles could
have near zero mass. Then specify harmonic bonds between

pairs of point particles on different ellipsoids to form a
chain. If the bond length R0 = 0.0 and the spring is stiff,
it will act like a chain. The GB potential will still act to
rotate the rigid bodies.

Steve