特有的自旋态自由度使得3d6组态离子化合物表现出比其他过渡金属化合物更丰富的物理现象。但体系中影响自旋态自由度的相互作用因素更多更复杂，且能量尺度相近。因此，人们对该类体系自旋态的判断及相关物理现象的解释存在很大争议。.本项目从钙钛矿结构的钴基化合物及梯状铁基化合物中选取代表性体系，采用密度泛函理论计算结合模型计算的方法对其自旋态以及自旋态转变从以下几方面进行研究：（1）研究晶场劈裂、洪特交换、自旋轨道耦合等对自旋态的影响并确定目标化合物的自旋态；（2）研究自旋态转变过程中相互作用因素的变化，给出自旋态转变的相图；（3）研究自旋态转变对材料物性的影响，从而对自旋态转变带来的材料物性的改变给出合理的解释。以上研究对探索自旋态自由度的物理机理具有重要意义，并有望为进一步实现自旋态调控奠定理论基础。

The 3d6 ion compounds exhibit numerous characteristics due to their own spin-state degree of freedom, which distinguishes them from other transition-metal compounds. Nonetheless，the factors which influence the spin-state issue are complicated and close in energy. So there are many controversies in the identification of the spin state and the comprehension of the corresponding physical phenomena..In this project，first-principles density functional theory calculations and model calculations are performed to investigate the spin state and spin-state transition in the perovskite cobaltates and the ladder iron compounds. Main contents are as follows.（1）Identify the spin state of the target compound by analyzing possible factors, such as the crystal-field splitting, Hund exchange， spin-orbit coupling, etc.（2）Explore the variations of factors in the spin-state transition and further demonstrate the phase diagram of spin-state transition.（3）Concern the influence of spin-state transition on the physical properties of materials in order to explain the variations of the physical properties which is caused by the spin-state transition. Our research will provide insights to the spin state degree of freedom and hints for the spin-state control.