Non-Born-Oppenheimer variational calculation of the ground-state vibrational spectrum of LiH ⁺

Very accurate, rigorous, variational, non-Born-Oppenheimer (non-BO) calculations have been performed for the fully symmetric, bound states of the LiH ⁺ ion. These states correspond to the ground and excited vibrational states of LiH ⁺ in the ground ²∑ ⁺ electronic state. The non-BO wave functions of the states have been expanded in terms of spherical N-particle explicitly correlated Gaussian functions multiplied by even powers of the internuclear distance and 5600 Gaussians were used for each state. The calculations that, to our knowledge, are the most accurate ever performed for a diatomic system with three electrons have yielded six bound states. Average interparticle distances and nucleus-nucleus correlation function plots are presented.