global cut off for L-J potentials

Dear All users:

How can I define a cut off for L-J (6-12) potential in this way?

rc = 2.5σij.

i and j are ch2 and ch3 and Au

The pair coeff command for pair_style lj/cut lets you
define a type-specific cutoff for each type I,J interaction.
Since you're also defining sigma in that command, you
can set rc to whatever you like.