diff --git a/examples/free-energy/free-energy.py b/examples/free-energy/free-energy.py
index 763b4f7e..f804d2f1 100644
--- a/examples/free-energy/free-energy.py
+++ b/examples/free-energy/free-energy.py
@@ -332,6 +332,8 @@ def PES_harm(x, y, z):
 plt.contour(X, Y, PES(X, Y, 0), levels=contour_levels)
 plt.show()
 
+# %%
+
 plt.title(r"$V^{\mathrm{harm}}(x,y,0)$")
 plt.xlabel(r"$x$ [a.u.]")
 plt.ylabel(r"$y$ [a.u.]")