20 research outputs found
Low-energy unphysical saddle in polynomial molecular potentials
Vibrational spectra of polyatomic molecules are often obtained from a
polynomial expansion of the adiabatic potential around a minimum. For several
molecules, we show that such an approximation displays an unphysical saddle
point of comparatively small energy, leading to a region where the potential is
negative and unbounded. This poses an upper limit for a reliable evaluation of
vibrational levels. We argue that the presence of such saddle points is
general.Comment: The preprint version of the published Mol. Phys. paper, 19 pages, 3
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