Modifying Cutoff Values


I was wondering if there was a way that I can change the lj/cut cutoff for different atom pairs interacting with each other. I want to do this because I have atoms of various sizes, and the coefficients change. I have the pair_coefficients that I need for each pair, but now I’m trying to figure out how to change the lj/cut off the some of these different pairs. I’m looking into the pair_modify command, however I was wondering how I can specify which atom pairs I want for each cutoff. Is there a way to do this with the pair_modify command (or at all)?



Yes! pair_coeff takes as an optional last argument a per-type-pair cut-off.
For example, if you want pairs of types 1-1 and 2-2 to interact fully but 1-2 only repulsively with an LJ potential, you would do
pair_style lj/cut 3.0
pair_coeff 1 1 1.0 1.0

pair_coeff 2 2 1.0 1.0

pair_coeff 1 2 1.0 1.0 1.1225