Studies on Electronic Structure of p Electron Systems and Nanostructure Materials Based on First-Prinsiples Methods for Strongly Correlated Electrons

该项目的目标是通过结合密度泛函理论和强相关晶格模型的求解器，开发一种用于强相关电子系统的电子结构计算的混合计算方法。通过建立该方法，我们将其应用于p电子系统和纳米结构材料。该混合方法由以下三个过程组成：（1）使用局域密度近似和引力波近似，通过密度泛函理论计算全局电子能带结构（2）通过下折叠消除和追踪高能尺度，并推导低能有效模型（3）通过可靠的低能求解器求解低能模型。该方案已应用于Sr2VO4。我们发现Sr2VO4位于金属-绝缘体相界附近，具有反铁磁序，并表现出复杂的自旋轨道序。接下来我们将其应用于YVO3的电子结构计算。它显示了绝缘基态，间隙为 0.9 eV，与实验间隙 1.0eV 一致。基于这些成功的结果，我们将该方案应用于 p 电子系统。在 p 电子系统中，我们采用了平面波基础。这已应用于有机导体 BEDT-TTF 化合物，并且我们导出了低能有效哈密顿量。我们还检查了激发光谱的效率。下折叠方案已应用于 GaAs 和 LiF，并计算了光导率。这些结果表明该方案正确捕获了激子效应。在这个项目中，还开发了几种不同类型的低能量求解器。除了路径积分重正化群之外，还开发了高斯基蒙特卡罗和改进的变分蒙特开罗方法，并且我们已经阐明这些方法可以用作高精度的低能量求解器，基本上没有负号问题。通过这些成果，目前已经建立了一种基于三阶段方案的新型强相关电子系统（包括p电子化合物）的电子结构计算方法。较少的

The goal of this project is to develop a hybrid computational method for electronic structure calculations of strongly correlated electron systems by combining the density functional theory and solvers for models of strongly correlated lattice models. By establishing the method, we apply it to p electron systems and nanostructure materials. This hybrid method consists of the following three procedures: (1) Calculate global electronic band structure by the density functional theory using the local density approximation and GW approximation (2) Eliminate and trace out the high-energy scale by downfolding and derive low-energy effective models (3) Solve the low-energy models by reliable low-energy solvers. This scheme has been applied to Sr2VO4. We have revealed that Sr2VO4 is near the metal-insulator phase boundary with antiferromagnetic order and shows complicated spin-orbital orders. Next we have applied to electronic structure calculation of YVO3. It shows the insulating ground state … More with the gap given by 0.9 eV, which is in agreement with the experimental gap, 1.0eV. Based on these successful results, we have applied this scheme to p-electron systems. In p-electron systems, we have employed the plane-wave basis. This has been applied to an organic conductor, BEDT-TTF compound and we have derived the low-energy effective Hamiltonian. We have also examined the efficiency for excitation spectra. The downfolding scheme has been applied to GaAs and LiF and the optical conductivity has been calculated. These results show that excitonic effects are correctly captured by this scheme. In this project, several different types of low-energy solvers have also been developed. In addition to the path integral renormalization group, Gaussian basis Monte Carlo and improved variational Monte Cairo methods have been developed and we have clarified that these method may be used as a highly accurate low-energy solver essentially without the minus sign problem. By these achievements, a new type of electronic structure calculation method based on the three-stage scheme for strongly correlated electron systems including p-electron compounds are now well established. Less