Internal vibrations of the Li(NH3)4+ complex analyzed from ab initio, density functional theory, and the classical spring network model

We report our theoretical findings regarding internal vibrations of the Li(NH 3) 4 (+) complex which have been studied using three different methods, namely, a classical spring network model, density functional theory, and ab initio Hartree-Fock plus M?ller-Plesset correlation energy correction truncated at second-order. The equilibrium Li...N and N...N distances are found to be 2.12 and 3.47 A, respectively, in good agreement with the experimental data. The theoretically determined vibrational frequencies of the lowest modes are in good agreement with those extracted from inelastic X-ray scattering measurements. From group theory considerations, the internal vibrations of Li(NH 3) 4 (+) complexes resemble those of a tetrahedral object. Further experimental investigation is suggested.