Theoretical characterization of the ground and optically excited states of alpha '-NaV2O5

The character of the ground and optically excited states was investigated by quantum chemical calculations. We propose a rung ground state with V 3d1xy-O 2p1y-V 3d1xy character, instead of the conventional picture of one unpaired electron shared by 2 V ions. The unpaired electron on O is low-spin coupled to the V d electrons and spin density is predicted to be localized on vanadium. The absorption peak at 0.9 eV is assigned to a state with similar orbital occupations but a different spin coupling scheme, resulting in spin density localized on the bridging oxygen.