Configuration interaction calculations on the nitrogen molecule

A contracted Gaussian basis set capable of describing about 63% of the correlation energy of N 2 has been used in a detailed configuration‐interaction calculation. Second‐order perturbation theory overestimated the correlation energy by 23–50% depending on how H 0 was chosen. Pair‐pair interaction affects the correlation energy by about 20% while quadruple excitations have an 8% effect.