diff --git a/dmff/classical/inter.py b/dmff/classical/inter.py
index 2ef172870..c4f2cff70 100644
--- a/dmff/classical/inter.py
+++ b/dmff/classical/inter.py
@@ -63,7 +63,7 @@ def get_energy(positions, box, pairs, epsilon, sigma, epsfix, sigfix, mscales):
 
             eps_m1 = jnp.repeat(epsilon.reshape((-1, 1)), epsilon.shape[0], axis=1)
             eps_m2 = eps_m1.T
-            eps_mat = jnp.sqrt(eps_m1 * eps_m2 + 1e-12)
+            eps_mat = jnp.sqrt(eps_m1 * eps_m2 + 1e-32)
             sig_m1 = jnp.repeat(sigma.reshape((-1, 1)), sigma.shape[0], axis=1)
             sig_m2 = sig_m1.T
             sig_mat = (sig_m1 + sig_m2) * 0.5