Direct configuration interaction and multiconfigurational self-consistent-field method for multiple active spaces with variable occupations.: II.: Application to oxoMn(salen) and N2O4

In a previous paper, a new direct configuration interaction method for multiple active spaces with variable occupations was described. The present article illustrates how this method may be applied to the oxoMn(salen) complex and the N2O4 molecule. In the first application it is shown how complete-active-space self-consistent-field wave functions of the oxoMn(salen) system may be approximated by a drastically reduced number of configurations with negligible loss of accuracy in terms of energetics. In the second application, to N2O4, it is demonstrated how the fully optimized reaction space wave function may be approximated and also how the recovery of dynamic correlation effects may be achieved. The best predictions of the structure (r(NN)=1.743 Angstrom, r(NO)=1.189 Angstrom, angle(ONO)=134.4degrees) and binding energy (D-e=16.0 kcal/mol) are both in very good agreement with experiment (r(NN)=1.756, r(NO)=1.191, angle(ONO)=134.46degrees, D-e=16.3 kcal/mol). (C) 2003 American Institute of Physics.