Theoretical study of the 7Sigma + u state of N2

Theoretical potentials for the ⁷Σ⁺_u state are reported using both extended Slater and Gaussian basis sets. Electron correlation is included using the interacting correlated fragments (ICF), the singles plus doubles configuration-interaction (SDCI), and the coupled-pair functional (CPF) approaches. Our best potential, corrected for basis set superposition errors, has a well depth of about 21 cm^-1 and an r_e of 7.52 bohr. The inclusion of the nitrogen 2s correlation significantly increases the well depth. These results are in reasonably good agreement with the empirical potential of Ferrante and Stwalley, and support the contention that spin-polarized atomic nitrogen should behave like a classical solid such as Ne. It is shown that the modified Buckingham potential used by Ferrante and Stwalley is consistent with our ab initio potentials if smaller values are used for the dispersion coefficients of nitrogen atom.