Ab initio potential curves for the X ${}^2{\mathrm{\Sigma }}_u^{+}$ and B ${}^2{\mathrm{\Sigma }}_g^{+}$ states of Be${}_2^{+}$: Existence of a double minimum

We report ab initio calculations of the X ${}^2{\mathrm{\Sigma }}_u^{+}$ and B $^2 \Sigma_{g}^+$statesoftheBe$_{2}^+$ dimer. Full valence configuration interaction calculations were performed using the aug-cc-pVnZ basis sets and the results were extrapolated to the CBS limit. Core-core, core-valence effects are included at the CCSDT/MTsmall level of theory. Two local minima, separated by a large barrier, are found in the expected repulsive B ${}^2{\mathrm{\Sigma }}_g^{+}$ state. Spectroscopic constants have been calculated and good agreement is found with the recent measurements of Merritt et al. Bound vibrational levels, transition moments and lifetimes have also been calculated.