DFT+Gutzwiller方法研究过渡金属氧化物

过渡金属氧化物因为表现出超导、庞磁阻、Mott金属绝缘体相变、重费米子行为、 Kondo效应等，一直是凝聚态物理的研究热点。同时，因为过渡金属氧化物中关联效应非常明显，这也是计算凝聚态物理的难点。.针对这个难题，我们在物理所方忠研究员领导下发展了能很好处理从强关联到弱关联体系整个区域与电子关联效应相关物理问题的DFT+Gutzwiller方法。我们将用该方法研究：1.Fe基超导体中的轨道波动对声子软化和磁矩等影响；2.新合成的 KCrF3 中关联效应和Jahn-Teller畸变导致的轨道和磁有序等问题；3.Ca2-xSrxRuO4等材料的金属-绝缘体相变问题。要解决上述问题就必须考虑关联效应导致的能带重整和轨道波动等问题，这是目前流行的LDA+U方法所不能处理的。LDA+DMFT方法虽能处理关联体系，但计算量太大，无法处理复杂的真实材料，而DFT+Gutzwille方法能够兼顾效率和准确。

Transition metal oxides(TMO) have been the research focus of condensed matter physics, since they show superconductivity, colossal magnetoresistance, Mott metal-insulator transition, heavy fermion behavior, Kondo effect. At the same time, it is a knotty issue because that the correlated effect is very important in the TMO systems. .To resolve this problem, we developed the DFT+Gutzwiller method,under the leadership of Fang Zhong.Our method can solve the above problem in the whole range from weak to strong correlated systems.We will use this method to study the followning three issues. Firstly, we will study the multiorbital nature of iron pnictides superconductors. The superconducting iron pnictides are interesting because of their different aspects to the cuprates:(1)they are multiorbital systems, where spin, orbital, and charge degrees of freedom are all active, while in cuprates an effective single band model can be established;(2)the electron correlation strength is intermediate, not as strong as that in cuprates. Due to the multiorbital nature, where interorbital interaction becomes important, the correlation in iron pnictides still plays a crucial role in determining not only the correct internal structure but also the correct electronic structure near the Fermi surface. Secondly, we will study the orbital and magnetical orderings of KCrF3.In this work, we will investigate the relations among the correlation, Jahn-Teller distortion, orbital and magnetical orderings. Thirdly, we will study the metal-insulator transition in Ca2-xSrxRuO4, where four electrons occupy the t2g orbitals(dxy,dyz,dzx) of Ru-4d. The occupation numbers of t2g orbitals are very important to determine its properties. However, occupation numbers are sensitive to the RuO6 octahedra distortion and electron correlation, which makes things complicated. To solve the above problems, we must consider the correlation effects induced orbitals fluctuation and band renormalization, which can not be sovled by the LDA+U method.In the LDA+DMFT method, although the correlation effect is well considered, the tremendous amount of calculations impede it be used in the real systems. Our DFT+Gutzwiller takes into account both the efficiency and the accuracy.