def METHOD_NAME():
    hitlist = []
    r2 = 2*Ratom
    r2 *= r2
    for i in range(Natoms):
        ai = apos[i]
        for j in range(i+1, Natoms) :
            aj = apos[j]
            dr = ai - aj
            if mag2(dr) < r2: hitlist.append([i,j])
    if (len(hitlist) > 0): process_collisions(hitlist)