Frozen-Core versus Fully-Correlated Configuration Interaction on the Ground and Lowest Excited States of N⁺ and N

Abstract

We present nonrelativistic frozen-core and fully-correlated configuration interaction calculations for the ground and lowest excited terms of N + ( 3 P and 1 D) and N( 4 S o and 2 D o ) belonging to the 2s 2 2p n configuration with n = 2 and n = 3 for N + and N, respectively. Both the a priori selected configuration interaction with truncation energy error and configuration interaction by parts techniques are employed to manage the wave function expansion and to handle the configuration interaction eigenvalue problem, respectively. Systematic comparisons between the frozen-core and fully-correlated configuration interaction energies and the corresponding excitation energies and the related ionization potential convergence with respect to the configuration interaction excitation level are reported. Comparison of our results for the total nonrelativistic energies, excitation energies, and ionization potential displays good improvement over previous theoretical results and very good agreement with the experiment.