Magnetostructural correlations and spin model of (VO)2P2O7

We report a theoretical density functional analysis of the exchange interactions in (VO)(2)P2O7 using molecular fragments. The calculations confirm that the magnetic structure must be described on the basis of linear dimer chains. The strongest exchange interaction is found through O-P-O bridges. The magnitude of the exchange parameters is governed not only by V-V distance but also by the whole structure along the superexchange pathway. The two chains present in the structure of (VO)(2)P2O7 are magnetically inequivalent. For the monoclinic phase of (VO)(2)P2O7, important variations in the calculated parameters for dimers with identical bridges are observed within one chain. The magnetic structure of this chain should be described not by two but by three or even four coupling constants.