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Zusammenfassung:
A new x-ray diffraction study of the one-dimensional spin-Peierls compound α′-NaV2O5 reveals a centrosymmetric (Pmmn) crystal structure with one type of V site, contrary to the previously postulated noncentrosymmetric P21mn structure with two types of V sites ( V+4 and V+5). Density-functional calculations indicate that NaV2O5 is a quarter-filled ladder compound with the spins carried by V-O-V molecular orbitals on the rungs of the ladder. Estimates of the charge-transfer gap and the exchange coupling agree well with experiment and explain the insulating behavior of NaV2O5 and its magnetic properties.
