Velocity autocorrelation function

Dear all,
This is the first time I tried to compute the VACF using Lammps, but I get zeros all the time for the four components of the outpout vector that the vacf command is meant to compute. I would appreciate any help to get around this problem. Here is the input file I use:

There is an example for computing self-diffusion using VACF in the examples/DIFFUSE folder. this is for 2d and reduced units and thus needs to be adapted. there also is an example and explanations in the documentation, but your input is missing some important steps required for it to work.

in addition, your simulation does not account for equilibration and i don’t think your system will melt since adding 1000K worth of kinetic energy into a perfect crystal will equilibrate into about 500K and i don’t think that nickel with the given potential will melt at such a low temperature and thus there should be no significant diffusion present and the limit of the integral over the VACF for t->oo should become 0.