How to include the potential energy in the granular simulation

Submitted by lin on Fri, 07/26/2013 - 11:18

I am using the sphere type for the granular simulation, how could I include the potential force in the simulation? I tired us the Pair_style hybrid gran/hertz/history lj/cut 2.5. But I get an error message” pair hybrid sub-style is not used”. Can someone help me out? thanks in advance