Hello everyone,

I want to model prolate ellipsoids and spheres using the Gay-Berne potential, but I have found the shape of the ellipsoids and spheres to be inconsistent depending on the type of particles that are interacting.

I have run a LAMMPS input file that moves a single sphere of shape (1, 1, 1) linearly towards a single prolate ellipsoid of shape (3, 5, 3). I have plotted the pairwise energy as a function of particle separation r. For sphere to ellipsoid side the pairwise energy is zero at r = 2.240 and for sphere to ellipsoid tip it is zero at r = 3.608. The correct values should be r = 2.0 and r = 3.0. For ellipsoid to ellipsoid side-to-side interaction the pairwise energy is zero at r = 3.0 and for side-to-tip it is zero at r = 4.125. The correct values should be r = 3.0 and r = 4.0.

Below is an excerpt of my input file.

set type 1 shape 1 1 1

set type 2 shape 3 5 3

pair_style gayberne 1.0 1.0 1.0 10.0

pair_coeff 1 1 1.0 1.0 1 1 1 0 0 0 2.5

pair_coeff 2 2 1.0 3.0 1 1 1 0 0 0 12.5

I have used LAMMPS version 16Feb16 and 4Nov16. I can send the plots of the pairwise energy and the input file if anyone is interested.

I am grateful for any feedback. Thanks!

Regards,

Olav Galteland

Norwegian University of Science and Technology