The theoretical determination of the B¹Π_u potential energy curve for Li₂

The Li₂ B 1Π_u potential energy curve has been calculated with a multiconfiguration SCF (MCSCF) wavefunction. Several different types of wavefunctions and basis sets have been examined and their accuracy determined. The most accurate wavefunction used predicts a binding energy of 0.3015 eV (0.08 eV above the experimental value of 0.385 eV) and a potential barrier of 0.0724 eV with its maximum at 10.6 bohr. It is argued that the theoretical value of the barrier is an upper bound to the experimental value. The long range behavior of the potential energy is found to match smoothly onto the form predicted from dispersion forces.