How fix brownian/asphere work?

LAMMPS
1

I am using fix brownian/asphere for creating the self propelled particle, i am keeping my particle mass 1.0 and shape sphere with diameter 1.0

“fix 1 mytype1 brownian/asphere {t} {seed} gamma_t_eigen 5.0 7.0 9.0 gamma_r_eigen 2.0 0.25 0.1 rng uniform”

“fix 2 mytype1 propel/self quat 100.0 qvector 1.0 1.0 1.0”

I am using the above two fixes for this. And timestep is 0.0001, I have small doubt about gamma_t_eigen and gamma_r_eigen. On what basis those values can be defined? Is there any dedicated calculation for that as they are not mentioned in documentation. Please clarify this

Thanks.

2

They are mentioned in the documentation and for particles like yours, that are spherical, it states that all three elements for each must be the same and that the ratio between gamma for translation and rotation must be at a specific ratio. For more details, you have to refer to the referenced publications.

3

I am basically using atom style ellipsoid to use fix quat command. I am making the particle sphere by providing shapex, shapey, shapez equal to 1.0. Then do i need to use different values for gamma_t_eigen, gamma_r_eigen to randomize the rotational motion? Is there any dependency of these values on rotational motion?

4

You have to figure out the answers by studying the referenced papers.