Dissociation energy and the lowest vibrational transition in LiH without assuming the non-Born–Oppenheimer approximation

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ABSTRACT The fundamental vibrational excitation energy and the dissociation energy of the main isotopologue of lithium hydride (LiH) are studied by the variational method using all-particle explicitly correlated Gaussian (ECG) basis sets. In this approach, electrons and nuclei are treated on equal footing, i.e. the Born–Oppenheimer approximation is not assumed. The leading relativistic () and the dominating part of the quantum electrodynamics () corrections to the energy levels are accounted for in the framework of the perturbation theory. The fundamental vibrational excitation energy and the dissociation energies obtained in the calculations are well within the error bars of the available experimental data.