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

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AbstractThe lowest doublet electronic state for the lithium trimer (12A′) 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 12A1 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 Møller–Plesset perturbation level of theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009