Full-range analytical potential for the a3 Σ+ state of LiNa: robust prediction of vibrational levels and scattering length

Abstract

Heteronuclear alkali diatomics in the lowest triplet state possess electric and magnetic dipoles, making them promising for quantum simulation of many-body physics. However, an analytical formula with physical transparency to describe the interaction potential of the heteronuclear alkali dimers involving Li atoms is still lacking. The present article shows that the Sheng–Tang–Toennies (STT) potential model with only two adjustable parameters describes the full-range potential energy curve (PEC) of the LiNa molecule in its lowest triplet electronic state (a³ Σ⁺) with high accuracy. Validation against high-accuracy ab initio data and experimental spectroscopy demonstrates exceptional agreement across all internuclear distances, with deviations <1% from ab initio calculations and Rydberg–Klein–Rees (RKR) potentials. The model achieves high-precision predictions for vibrational energy levels, which show a root-mean-square error (RMSE) of 0.1965 cm⁻¹ (11 observed states), and the s-wave scattering length was calculated as −71.28 a.u., consistent with experimental bounds (−76 ± 5 a.u.). This work demonstrates that the STT model is effective for modeling the PEC of heteronuclear alkali dimers involving a Li atom.