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

ABSTRACT

The fundamental vibrational excitation energy and the dissociation energy of the main isotopologue of lithium hydride (${}^7$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 ($\sim {\alpha }^2$) and the dominating part of the quantum electrodynamics ($\sim {\alpha }^3$) 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.

GRAPHICAL ABSTRACT

KEYWORDS:

• Lithium hydride
• explicitly correlated gaussians
• non-Born–Oppenheimer calculations
• relativistic corrections

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Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work has been supported by Nazarbayev University (faculty development grant no. 021220FD3651) and the National Science Foundation (grant no. 1856702). L.A. acknowledges the support of the Centre for Advanced Study (CAS), the Norwegian Academy of Science and Letters, in Oslo, Norway, which funds and hosts our research project titled: Attosecond Quantum Dynamics Beyond the Born–Oppenheimer Approximation, during the 2021–22 academic year. The authors are grateful to the University of Arizona Research Computing and Nazarbayev University Academic Computing for providing computational resources for this work.