Charge-orbital Ordering, Magnetic State, and Exchange Couplings in Quasi-One-Dimensional Vanadate V6O13

Charge and orbital ordering, magnetic state, and exchange couplings in quasi-one-dimensional vanadate V 6 O 13 , a potential cathode material for Li-ion batteries, are investigated using the density functional theory with Coulomb interaction correction method (DFT + U ). While the difference between orbital occupancies of V 4+ (with a nominal electronic configuration) and V 5+ ions is large and gives direct evidence for charge and orbital ordering, the screening is so effective that the total charge disproportionation is rather small. Our results show that the occupied states of V 4+ ions in the single V–V layer form a spin-singlet molecular orbital, while the rest half of V 4+ ions in the structurally distinct double V–V layers order antiferromagnetically in the low-temperature insulating phase of V 6 O 13 . We conclude that the metal-insulator transition and low-temperature magnetic properties of V 6 O 13 involve the spin-Peierls transition assisted by orbital ordering and concomitant distortions of the crystal structure.