A correlator product state study of molecular magnetism in the giant   Keplerate Mo72Fe30
  We have studied the properties of the giant Keplerate molecular magnet Mo72Fe30, as a function of applied magnetic field, using the correlator product state (CPS) tensor network ansatz. The magnet is modeled with an S = 5/2 antiferromagnetic Heisenberg Hamiltonian on the 30-site icosidodecahedron lattice, a model for which exact diagonalization is infeasible. The CPS ansatz produces significant improvements in variational energies relative to previous studies using the density matrix renormalization group, a result of its superior ability to handle strong correlation in two dimensional spin systems. The CPS results reaffirm that the ground state energies adhere qualitatively to the parabolic progression of the rotational band model (RBM), but show important deviations near 1/3 of the saturation field. These deviations predict anomalous behavior in the differential magnetization and heat capacity that cannot be explained by the RBM alone. Finally, we show that these energetic deviations originate from a qualitative change in the ground state that resembles a finite size analogue of a phase transition. 
Eric Neuscamman and Garnet Kin-Lic Chan
cond-mat.str-el