Complex self-consistent field and multireference single- and double-excitation configuration interaction calculations for the 2Πg resonance state of N2-

Self-consistent field and multireference single- and double-excitation configuration interaction calculations employing the complex basis function technique are carried out for the (2)Pi(g) resonance state of the N-2(-) molecule as well as several other anionic resonance states in the neighboring energy region. The results of calculations employing the same method for the S-1 (2s(2)) state of the He atom and the (1)Sigma(+)(g) (sigma(2)(u)) state of the H-2 molecule are found to be in good agreement with those of earlier work. The present theoretical treatment has succeeded for the first time in satisfying the rigorous criterion of the complex variational principle in computing the N-2(-) resonance states, namely, a cusp in the plots of real versus imaginary components of the corresponding complex energies has been located at each internuclear distance. On this basis, it is found that the open-shell orbital in the lowest-energy adiabatic N-2(-) resonance state of (2)Pi(g) symmetry changes its character from quite compact at large internuclear distance to relatively diffuse for r < 2.3a(0). This is in contrast to all previous theoretical treatments of this system that have not rigorously satisfied the complex variational principle in their determination of this wave function. (c) 2006 American Institute of Physics.