where ZA and ZB correspond to the mass of nuclei A and B, respectively. In Equation , the first and second terms represent the kinetic energies of electrons (Te) and kinetic energies of nuclei (Tn), respectively. Third term corresponds to the electron-nuclei coulombic interaction (Ven) and fourth term represents the nuclei-nuclei coulombic repulsion (Vnn). The last term of the above equation corresponds to electron-electron coulomb repulsion (Vee). Therefore, Equation 2 can be written as;