Potential Energy Surface of the 12A′ Li2+Li Doublet Ground State

The lowest doublet electronic state for the lithium trimer (1(2)A') 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 1(2)A' 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 1(2)E' surface into the 1(2)A(1) and 1(2)B(2) states is investigated using a combination of both CASSCF and FCI levels of theory. Additionally, preliminary calculations of the 1(2)A '' surface are also presented using second order spin restricted open-shell Moller-Plesset perturbation level of theory. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 3112-3119, 2009