扩展Hubbard模型局域方法的四阶近似

应用局域方法四阶近似，计算了扩展Ｈｕｂｂａｒｄ模型顺磁相的相关性，局域磁矩和反铁磁极化。计算表明，当电子密度ｎ较小时，尽管Ｕ和Ｗ可以很大，对三阶近似结果仍没有明显修正，只有当ｎ，Ｕ和Ｗ都较大时，对三阶近似结果的修正才变得明显。

Local Fourth-Order Approximation for Extended Hubbard Model

Local fourth-order approximation is introduced into the extended Hubbard model to calculatecorrelation energy,local moments and antiferromagnetic polarization in paramagnetic phase.The results indicate that the fourth-order modification is not significant to third-order approximation if electronic density n issmall in spite of the large value of U or W. However,such a modification will become obvious only if the values of n,U and W are all great.