Applicability of the unmodified MNDO theory to the low-lying excited singlet and triplet states is tested through an adaptation of the single excitation electron-hole potential (EHP) method to the theory. The method is both structurally and computationally very simple and has the useful feature of orbital picture for the excited states. The agreement, in the transition energies and also in the relative ordering of various excited states, obtained by our method and from the extended CI method, is very good. There is some problem in convergence arising out of symmetry breaking in cases of degeneracy in the ground state SCF wavefunction.
Volume 134, 2022
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