Abstract
Single-molecule magnets of the type V-15(K-6[V15As6O42(H2O)].8H(2)O) have attracted a great deal of attention recently, being promising systems for studying low-temperature spin-relaxation and quantum-spin tunneling. To understand in detail the internal magnetic and electronic structure, and the intramolecular interactions responsible for the formation and low-energy excitations in V-15 molecules, we have performed electronic structure calculations using the LSDA+U approach. The calculated values of magnetic moments and charge states of vanadium ions agree well with experiments, thus confirming the V4+ state of vanadium ions with a well-defined spin 1/2. We found that the account of the on-site Coulomb repulsion is important for correct description of V-15 internal properties; in particular, for the values of the on-site repulsion parameter Usimilar to4-5 eV, we can achieve good agreement with known properties of V-15, such as the temperature dependence of susceptibility, and the energies of the low-lying eigenstates of the spin Hamiltonian.
