orce felds Atomic systems. U=∑W)∑∑MGF)∑∑∑vFFF片 j>i k>j> where ul, u, and u3 are respectively one-body two-body three-body interaction potentials Pair potential models are widely used in simulations Model interaction potentials Hard-sphere potential u(rForce fields ( ) ( , ) ( , , ) ... 1 2 3 = +  +   +     u r u r r u r r r k k j i i j i j i j j i i i i i U       Atomic systems: where u1 , u2 and u3 are respectively one-body, two-body, three-body interaction potentials. Pair potential models are widely used in simulations. Model interaction potentials Hard-sphere potential: u HS(r) =  r < s 0 r > s r u(r) s