New methods for electronic excited states of solids using localized basis

我们发展了一种利用高斯基组计算聚合物激发态的第一性原理方法，并提出了研究固体激发态的其他有效方法，具体如下：1.提出了一种基于高斯基的Hartree-Fock晶体轨道理论、耦合团簇理论和运动方程耦合团簇理论计算一维周期体系激发态的方法。该方法可以高精度地考虑电子相关效应，从而计算聚合物的激发态。通过自旋自由密度泛函计算，发现聚二乙炔中乙炔和丁三烯结构之间存在两个自旋密度波态。3.基于局域电子-空穴相互作用假设，利用含时密度泛函理论和Bethe-Salpeter方程，提出了一种简化的激发态计算方法。4.利用动力学平均场理论和GW近似，提出了一种计算强关联材料激发态的方法。该方法成功地应用于镍的电子能带结构的研究。从二维Hubbard模型出发，得到了含时密度泛函理论中的交换关联核(FXC)。通过与理论激发谱的比较，证明了FXC在多体激发的能区具有很强的能量依赖性。

We have developed a first-principles method for excited states of polymers using gaussian basis sets and proposed other efficient methods for studying excited states of solids, as summarized as the following.1.A computational method has been developed to calculate excited states of one-dimensional periodic systems using Hartree-Fock crystal orbital theory with gaussian basis sets, coupled-cluster theory, and equation-of-motion coupled-cluster theory. The method makes it possible to calculate excited states of polymers by taking electron correlation effects into accounts with high accuracy. The calculated excitation energies of polyethylene were well comparable with experiments.2.Two spin-density wave states were found in polydiacetylene between acetylene and butatriene structures from spin-unrestricted density functional calculations. The corresponding potential energy functions were different.3.A simplified computational method for excited states was proposed using time-dependent density functional theory and Bethe-Salpeter equation based on the assumption of a local electron-hole interaction.4.A computational method for excited states of strongly-correlated materials was proposed using dynamical mean-field theory and GW approximation. The method was successfully applied to electronic band structure of Ni. The agreement with the experimental band energies was excellent.5.Exchange-correlation kernel (fxc) in time-dependent density-functional theory was obtained from two-dimensional Hubbard model. By comparison with theoretical excitation spectrum it was demonstrated that fxc has strong energy dependence in the energy regions where there are many-body excitations.