Large electron correlation effect leading to BeBe bond

The bonding of the beryllium diatomic molecule (Be₂) in the ground state is exclusively made from the electron correlation effect. Unlike the ordinary van der Waals bond, where the electron correlation of the dispersion type makes weak bond energy (D_e) at large bond distance (R_e), the BeBe bond is surprisingly strong with D_e = 830 cm^?1 and R_e = 245 pm. This paper presents in an analytical way the different electron correlation effects with the corresponding spectroscopic data.