New methods for electronic excited states of solids using localized basis

我们利用高斯基集开发了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，总结如下。利用具有高斯基集的Hartree-Fock晶体轨道理论、耦合簇理论和运动方程耦合簇理论，建立了一维周期系统激发态的计算方法。该方法考虑了电子相关效应，使聚合物的激发态计算具有较高的精度。计算得到的聚乙烯激发能与实验结果吻合较好。通过不受自旋限制的密度泛函计算，在聚二乙炔和丁烯结构之间发现了两种自旋密度波态。对应的势能函数不同。基于局域电子-空穴相互作用的假设，利用时变密度泛函理论和Bethe-Salpeter方程，提出了激发态的简化计算方法。利用动力学平均场理论和GW近似，提出了一种强相关材料激发态的计算方法。该方法成功地应用于镍的电子能带结构。所得能带能与实验结果吻合良好。基于二维Hubbard模型，得到了时变密度泛函理论中的交换相关核。通过与理论激发谱的比较，证明了fxc在存在多体激发的能量区具有较强的能量依赖性。

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.