Highly accurate ab initio calculation of the interaction potential for two sodium atoms with parallel spins

The potential energy curve for Na2 in the a 3Σu+ state is characterized by the Re and De parameters which are found to be equal to 5.192 Å and 177.7 cm−1, respectively, at the coupled cluster level of theory with single, double, and noniterative triple excitations. It is argued that the theoretical value of Re may be more accurate than that extracted from the experimental data [Friedman-Hill and Field, J. Chem. Phys. 96, 2444 (1992)].