Hi all,
I am just working on a system consisting of two types of particles with different shapes. The first kind is a simple sphere with radius one and the other one is an ellipsoid with radii 3 1 1. The potential I’m going to use is gayberne. I am confused setting the potential parameters. I have read the manual but I think it contradicts with lammps example “ellipse”. I don’t know what is the relationship between potential parameters and desired ellipsoid radii.
Let an ellipsoid have radii a b and c. Consider the following lines:
shape a b c
…
pair_coeff 1 * epsilon sigma x1 x2 x3 y1 y2 y3
How should I set epsilon, sigma, x1, x2 and x3 in order to apply the different radii of ellipsoid in potential?
Thank you in advance
M. Baghery
Hi all,
mehrdad,
I am just working on a system consisting of two types of particles
with different shapes. The first kind is a simple sphere with radius
one and the other one is an ellipsoid with radii 3 1 1. The potential
I'm going to use is gayberne. I am confused setting the potential
parameters. I have read the manual but I think it contradicts with
lammps example "ellipse". I don't know what is the relationship
between potential parameters and desired ellipsoid radii.
Let an ellipsoid have radii a b and c. Consider the following lines:
shape a b c
...
pair_coeff 1 * epsilon sigma x1 x2 x3 y1 y2 y3
How should I set epsilon, sigma, x1, x2 and x3 in order to apply the
different radii of ellipsoid in potential?
i would rather say that _your_ example contradicts bother
the ellipse example and what is in the LAMMPS manual.
the syntax for shape is:
shape <type> <a> <b> <c>
i.e. it takes four arguments and similarly there are
no x1 x2 x3 y1 y2 y3 parameters for the pair_coeff
command. in my (up-to-date) version of LAMMPS the ellipsoid
example matches the documentation well.
what version of LAMMPS are you using?
cheers,
axel.
I talked to Mike Brown about this. The GB standard practice
is to define sigma as the min of the 3 shape diams, though
you don't have to. This is different than the RE-squared
potential where sigma is the size of the small sphere you
are integrating over, typically 1 regardless of the size
of the much bigger ellipsoid.
Note that for I,J interactions sigma can be mixed or
specified directly with a pair_coeff command.
I've amended the doc pages to reflect this guidance.
Steve