High-accuracy <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal">Rb</mml:mi><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:math> interaction potentials based on coupled-cluster calculations

This work discusses a protocol for constructing highly accurate potential energy curves (PECs) the lowest two states of Rb$_{2}^+$, i.e. $X\,{}^2{\Sigma}{_g^+}$ and $(1) {}^2\Sigma{_u^+}$, using an additivity scheme based on coupled-cluster theory. The approach exploits findings our previous [J. Schnabel, L. Cheng A. K\"ohn, J. Chem. Phys. 155, 124101 (2021)] to avoid unphysical repulsive long-range barrier occurring symmetric molecular ions when perturbative estimates higher-order cluster operators are employed. Furthermore, care was taken reproduce physically correct exchange splitting $X {}^2{\Sigma}{_g^+}$ {}^2{\Sigma}{_u^+}$ PECs. accuracy computational is benchmarked ionization energies Rb spectroscopic constants as well vibrational levels $a {}^3{\Sigma}{_u^+}$ triplet state Rb\textsubscript{2}. We study high-level correlation contributions, relativistic effects inner-shell contributions find very good agreement with experimental reference values atomic binding Rb$_{2}$ in $a\,{}^3{\Sigma}{_u^+}$ state. Our final best estimate Rb$_{2}^+$ including zero-point $D_0 = 6179\,\mathrm{cm}^{-1}$ estimated error bound $\mathcal{O}(\pm 30\,\mathrm{cm}^{-1})$. value smaller than experimentally inferred lower bond $D_0\ge 6307.5\,\mathrm{cm}^{-1}$ [Bellos et al., Rev. A 87, 012508 (2013)] will require further investigation. For shallow 78.4\,\mathrm{cm}^{-1}$ $\pm 9\,\mathrm{cm}^{-1}$ computed.