• There is a Coulomb energy term \( a_3\frac{Z^2}{A^{1/3}} \). The electric repulsion between each pair of protons in a nucleus yields less binding.
• There is an asymmetry term \( a_4\frac{(N-Z)^2}{A} \). This term is associated with the Pauli exclusion principle and reflectd the fact that the proton-neutron interaction is more attractive on the average than the neutron-neutron and proton-proton interactions.

We could also add a so-called pairing term, which is a correction term that arises from the tendency of proton pairs and neutron pairs to occur. An even number of particles is more stable than an odd number. Performing a least-square fit to data, we obtain the following numerical values for the various constants

• \( a_1=15.49 \) MeV
• \( a_2=17.23 \) MeV
• \( a_3=0.697 \) MeV
• \( a_4=22.6 \) MeV