What is the energy of the London dispersion force holding together two atoms of the same element?
Polarisability as used here has dimensions of volume. The London formula is $$U \approx -\frac{3}2\frac{I_aI_b}{I_a+I_b}\frac{\alpha _a \alpha _b}{r^6}$$  for two species a and b so you just need to square $\alpha$.