Request for a technical problem in LAMMPS

Dear all,

I am trying to simulate a system composed of rod-like active particles ( I am using 10Aug15 version). To do this, I have set particles in a row for every rod-like particles and made them rigid as rigid bodies. I have set heads and tails atoms as two separated groups. Then, I need to obtain unit vectors in direction of rod’s axis. The problem is being atom_style of fix addforce command as well as variable … atom … . To obtain unit vectors in direction of rod’s axis I have tried on two ways:

I think you are saying you want to compute and add forces to rigid bodies
which are based on the current orientation of the bodies as determined
by their orientation. I don’t see an easy way to do that with

atom_style variables. I suggest you write your own
fix which can do whatever you want. You could also write your
own compute orient/chunk, similar to compute com/chunk which
calculates the orientation of each chunk (rigid body), which the
new fix could invoke to get the orientation vectors.