CI calculations for the inversion barrier of ammonia

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Abstract
CI calculations have been performed for the planar and pyramidal forms of ammonia using a near‐Hartree‐Fock basis set of STO's. Full single and double excitation valence Cl shows that the correlation energy for the barrier is small, less than 0.5 kcal/mole, a result in agreement with experiment. Several more approximate methods were found to yield similar results; however, the first‐order wavefunction method gave a result of 2.5 kcal/mole for the correlation energy of the inversion barrier. Fully optimized SCF and CI calculations were also performed for minimum basis sets: In this case it was found that the CI results were much worse than the SCF.