### Abstract

Generalized Gutzwiller-type trial ground states for the Hubbard model are considered, which include extra variational parameters to control the nearest-neighbour charge-charge, charge-spin, and spin-spin correlations. The correlation between doubly occupied and empty sites is found to be particularly important. The results for the large-U regime show qualitative improvement when compared to the predictions of the simple Gutzwiller Ansatz: We get the correct order of magnitude for the energy density, and the band state occupation number is found to be a monotonically decreasing function, with the leading term corresponding to that of the t/U-expansion. We find that to get the small-U limit right, the pair-correlated Ansatz has to be used in conjunction with a cluster Gutzwiller approximation, and introduce a four-site cluster approximation which gives promising results. We argue that small-cluster Gutzwiller approximations get accurate in the limit of large lattice dimensionality.

Original language | English |
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Pages (from-to) | 125-129 |

Number of pages | 5 |

Journal | Physica Scripta |

Volume | 1989 |

Issue number | T29 |

DOIs | |

Publication status | Published - Jan 1 1989 |

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### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics
- Mathematical Physics
- Condensed Matter Physics

### Cite this

*Physica Scripta*,

*1989*(T29), 125-129. https://doi.org/10.1088/0031-8949/1989/T29/023