Publication: Extended Hubbard model on a C_20 molecule

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Title	Extended Hubbard model on a C_20 molecule
Authors/Editors*	Fei Lin, Erik Sorensen, Catherine Kallin, John Berlinsky
Where published*	Journal of Physics: Condens. Matter
How published*	Journal
Year*	2008
Volume	19
Number	-1
Pages	456206
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Abstract	The electronic correlations on a C_20 molecule, as described by an extended Hubbard Hamiltonian with a nearest neighbor Coulomb interaction of strength V, are studied using quantum Monte Carlo and exact diagonalization methods. For electron doped C_20, it is known that pair-binding arising from a purely electronic mechanism is absent within the standard Hubbard model (V=0). Here we show that this is also the case for hole doping for 0< U/t <=3 and that, for both electron and hole doping, the effect of a non-zero V is to work against pair-binding. We also study the magnetic properties of the neutral molecule, and find transitions between spin singlet and triplet ground states for either fixed U or V values. In addition, spin, charge and pairing correlation functions on C_20 are computed. The spin-spin and charge-charge correlations are very short-range, although a weak enhancement in the pairing correlation is observed for a distance equal to the molecular diameter.