Multistate density functional theory applied with 3 unpaired electrons in 3 orbitals: The singdoublet and tripdoublet states of the ethylene cation

摘要

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 (pi,pi*) 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.