Potential energy surface of the 1²A′ Li₂₊Li doublet ground state

The lowest doublet electronic state for the lithium trimer (1 ²A′) is calculated for use in three-body scattering calculations using the valence electron FCI method with atomic cores represented using an effective core potential. It is shown that an accurate description of core-valence correlation is necessary for accurate calculations of molecular bond lengths, frequencies and dissociation energies. Interpolation between 1²A' ab initio surface data points in a sparse grid is done using the global interpolant moving least squares method with a smooth radial data cutoff function included in the fitting weights and bivariate polynomials as a basis set. The Jahn-Teller splitting of the 1²E' surface into the 1 ²A₁ and 1²B₂ states is investigated using a combination of both CASSCF and FCI levels of theory. Additionally, preliminary calculations of the 1²A" surface are also presented using second order spin restricted open-shell Moøler-Plesset perturbation level of theory.