Electronic Structure and Exchange Interactions of Na${}_2$V${}_3$O${}_7$

Abstract

We have performed first-principle calculations of the electronic structure and exchange couplings for the nanotube compound Na${}_2$V${}_3$O${}_7$ using the LDA+U approach. Our results show that while the intra-ring exchange interactions are mainly antiferromagnetic, the inter-ring couplings are {\it ferromagnetic}. We argue that this is a consequence of the strong hybridization between filled and vacant 3d vanadium orbitals due to the low symmetry of Na${}_2$V${}_3$O${}_7$, which results into strong - and often dominant - ferromagnetic contributions to the total exchange interaction between vanadium atoms. A comparison with results of previous works is included.

6 pages, 5 figures