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在密度泛函理论框架下的局域密度近似方法 (LDA)能够准确地给出广延态电子体系的基态电子结构 ,是研究复杂体系的电子结构的一种非常成功的方法。由于这种方法不含参数 ,被广泛地用于微观体系的研究。但是 ,在处理的体系中含有局域电子时 ,由于方法的局限 ,给出的结果与光电子谱等试验结果符合得并不好。LSDA +U方法是在局域自旋密度近似的框架下 ,结合模型哈密顿方法 ,对局域电子采用哈伯德模型描述 ,用以改进局域密度近似计算的一种方法。本文利用局域密度近似下的离散变分团簇方法 (DVM )对于内嵌稀土原子的富勒烯Er2 @C82 、Tm @C82 的电子结构进行了第一性原理的计算。对于体系中所含的稀土原子存在强关联的 4f电子 ,在LDA方法计算的基础上 ,考虑 4f电子在位库仑作用 ,用LSDA +U方法研究了上述体系 ,得到了可以和XPS和吸收谱相比较的结果。
The density approximation method (LDA) under the framework of density functional theory can give the ground state electronic structure of the extended electronic system accurately and is a very successful method to study the electronic structure of the complex system. Because this method does not contain parameters, it is widely used in micro-system research. However, when the system contains localized electrons, the results given are not in good agreement with the experimental results such as photoelectron spectroscopy because of the limitations of the method. LSDA + U method is based on the local spin density approximation framework, combined with the model Hamiltonian method, the local electron using Hubbard model description, to improve the approximation of local density of a method. In this paper, the first-principles calculations of the electronic structures of rare earth-doped fullerenes Er2 @ C82, Tm @ C82 were carried out using the discrete variational cluster method (DVM) with local density approximation. Based on the calculation of LDA method, we consider the Coulomb interaction of 4f electrons in the presence of 4f electrons which are strongly related to the rare earth atoms contained in the system. The above system was studied by LSDA + U method, The result of the comparison.