import numpy as np
import matplotlib.pyplot as plt

s1 = 5
s2 = 5.2
e1 = 65
e2 = 100

s12 = 0.5 * (s1 + s2)
e12 = np.sqrt(e1*e2)

u_LJ = lambda r, s, e: 4 * e * ((s/r)**12 - (s/r)**6)

r_list = np.linspace(4.9, 7, 100)

plt.plot(r_list, u_LJ(r_list, s1, e1), label='1')
plt.plot(r_list, u_LJ(r_list, s2, e2), label='2')
plt.plot(r_list, u_LJ(r_list, s12, e12), label='12')
plt.legend()
plt.show()