Ultracold polar and magnetic ${}^{23}\mathrm{Na}{}^6\mathrm{Li}$ molecules in the rovibrational ground state of the lowest triplet $a^3{\mathrm{\Sigma }}^{+}$ electronic state have been recently produced. Here, we calculate the electronic and rovibrational structure of these 14-electron molecules with spectroscopic accuracy ($<0.5{\mathrm{cm}}^{-1}$) using state-of-the-art ab initio methods of quantum chemistry. We employ the hierarchy of the coupled-cluster wave functions and Gaussian basis sets extrapolated to the complete basis set limit. We show that the inclusion of higher-level excitations, core-electron correlation, relativistic, QED, and adiabatic corrections is necessary to accurately reproduce scattering and spectroscopic properties of alkali-metal systems. We obtain the well depth, $D_e=229.9\left(5\right){\mathrm{cm}}^{-1}$, the dissociation energy, $D_0=208.2\left(5\right){\mathrm{cm}}^{-1}$, and the scattering length, $a_s=-{84}_{-41}^{+25}\mathrm{bohr}$, in good agreement with recent experimental measurements. We predict the permanent electric dipole moment in the rovibrational ground state, $d_0=0.167$(1) D. These values are obtained without any adjustment to experimental data, showing that quantum chemistry methods are capable of predicting scattering properties of many-electron systems, provided relatively weak interaction and small reduced mass of the system.

• Received 26 March 2020
• Accepted 20 July 2020

DOI:https://doi.org/10.1103/PhysRevA.102.020801