Multistate density functional theory (MSDFT) is extended to facilitate treatment of situations involving more than two open-shell electrons. The method is applied to determine energies for the two doublet state (tripdoublet and singdoublet) and the quartet-state components that arise when two electrons of one spin type and one electron of the other singly occupy three orbitals. A test system, the (π,π*) excitation of the ethylene cation, is utilized, with MSDFT delivering energies that are numerically superior to those from time-dependent density-functional theory (TD-DFT) and states free from spin contamination.
Bibliographical noteFunding Information:
We thank the National Natural Science Foundation of China for supporting this research under grants 11674212 and 91541124 , and the Ministry of Science and Technology under grant 2018YFB0203400 .
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