Displacement of atoms

Dear LAMMPS users,

I am trying to simulate a collision cascade with a uranium atom. I was trying to calculate how many atoms are in the cascade and this is by checking how many atoms were displaced with more than 2 Ang, my problem is when I used compute displace/atom, all atoms were displaced with large numbers despite that the radiation effect was localized in the center of the supercell only. In addition to that, when I checked the atom coordinated in the equilibration section (before irradiation), the atoms were also displaced by high values (more than the equilibrium distance).

Am I understanding the displacement concept wrongly? isn’t it the vector whose length is the shortest distance from the initial to the final position of a point and it can be used to detect the if an atom is a part of a collision cascade or not? or is it all about coordinates the lammps is using to calculate the displacement?

I viewed my system and there is no amorphization and the disturbance is cell centered localized…

I hope if you can help and thank you in advance…

*****Computing the displacement of atoms *****

compute disp all displace/atom
fix 9 all store/state 1 c_disp[4]

dump disp all custom 100 disp.dat type id mass xu yu zu c_disp[4]