Here, H SP , the S-PS nucleus-electron coupling Hamiltonian is defined as i(G F / √ 2)Zk s γ 0 γ 5 ρ N (r). The G F here is the Fermi constant, and ρ N (r) denotes the nuclear charge density normalized to unity. The fundamental S-PS nucleon-electron interaction, k s is defined as follows: Zk s =(Zk s,p +Nk s,n ), where N denotes the number of neutrons, and k s,p and k s,n are the electronproton and electron-neutron coupling constant, respectively.