The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory

Mu Jeng Cheng, Robert J. Nielsen, Jamil Tahir-Kheli, William A. Goddard

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

We have studied the magnetic structure of the high symmetry vanadyl pyrophosphate ((VO)2P2O7, VOPO), focusing on the spin exchange couplings, using density functional theory (B3LYP) with the full three-dimensional periodicity. VOPO involves four distinct spin couplings: two larger couplings exist along the chain direction (a-axis), which we predict to be antiferromagnetic, JOPO = -156.8 K and JO = -68.6 K, and two weaker couplings appear along the c (between two layers) and b directions (between two chains in the same layer), which we calculate to be ferromagnetic, Jlayer = 19.2 K and Jchain = 2.8 K. Based on the local density of states and the response of spin couplings to varying the cell parameter a, we found that JOPO originates from a super-exchange interaction through the bridging -O-P-O- unit. In contrast, JO results from a direct overlap of 3dx2 - y2 orbitals on two vanadium atoms in the same V2O8 motif, making it very sensitive to structural fluctuations. Based on the variations in V-O bond length as a function of strain along a, we found that the V-O bonds of V-(OPO)2-V are covalent and rigid, whereas the bonds of V-(O) 2-V are fragile and dative. These distinctions suggest that compression along the a-axis would have a dramatic impact on JO, changing the magnetic structure and spin gap of VOPO. This result also suggests that assuming JO to be a constant over the range of 2-300 K whilst fitting couplings to the experimental magnetic susceptibility is an invalid method. Regarding its role as a catalyst, the bonding pattern suggests that O2 can penetrate beyond the top layers of the VOPO surface, converting multiple V atoms from the +4 to +5 oxidation state, which seems crucial to explain the deep oxidation of n-butane to maleic anhydride.

Original languageEnglish
Pages (from-to)9831-9838
Number of pages8
JournalPhysical Chemistry Chemical Physics
Volume13
Issue number20
DOIs
Publication statusPublished - 2011 May 28

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Fingerprint Dive into the research topics of 'The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory'. Together they form a unique fingerprint.

  • Cite this