Calculation Of Intercalated Transition Metal Chalcogenide Compounds

In this paper,the structural properties,stability,electronic structure and magnetic properties of two-dimensional transition metal VIA group compounds intercalated with 3d or 4d transition metal elements are systematically investigated using first-principles calculations based on density generalized theory,and several structurally stable two-dimensional intercalated materials with ferromagnetic semimetallic and semiconducting properties are found by predicting the magnetic phase transition temperature with the Heisenberg model and Monte Carlo simulations.Firstly,the stability,electronic structure and magnetic properties of the self-intercalated two-dimensional materials M_2+σX₄（M=V,Cr,Mn,Fe;X=S,Se,Te）were investigated computationally,from which six stable materials with Curie temperature higher than room temperature were found,namely:Mn_2+1/4Se₄（Tc～327K）,Mn_2+1/3S₄（Tc～322K）,Mn_2+2/3S₄（Tc～313K）,Mn_2+2/3Se₄（Tc～360K）,Mn_2+2/3Te₄（Tc～472K）,and Fe_2+2/3S₄（Tc～360K）.Further studies showed that Fe_2+2/3S₄is an antiferromagnetic semiconductor,while Mn_2+1/4Se₄,Mn_2+1/3S₄,Mn_2+2/3S₄and Mn_2+2/3Se₄are ferromagnetic semimetals.The stability,electronic structure and magnetic properties of two-dimensional transition metal VIA group compounds MX₂-MX-MX₂（M=V,Cr,Mn,Fe;X=S,Se,Te）with the presence of MX chains in two MX₂layers have also been studied computationally.The results show that all these compounds have negative formation energies and also have the potential to be synthesized experimentally.Among them,VSe₂-VSe-VSe₂and Cr Se₂-Cr Se-Cr Se₂are kinetically stable.The calculations also show that Mn S₂-Mn S-Mn S₂and Mn Se₂-Mn Se-Mn Se₂exhibit ferromagnetic semimetallic properties,while Cr S₂-Cr S-Cr S₂is able to transform into ferromagnetic semimetals under applied stress.Finally,the structural properties,stability,electronic structure,and magnetic properties of the two-dimensional transition metal VIA group compounds Mo_σM₂X₄and W_σM₂X₄（M=V,Cr,Mn,Fe;X=S,Se,Te）were also investigated,and our results showed that their stable structures are both ordinary magnetic metals,where Mo_1/4Mn₂Se₄（Tc～365 K）and Mo_2/3Fe₂S₄（Tc～414K）have higher Curie temperatures.The research in this thesis not only enriches the variety of intercalated two-dimensional magnetic materials,but also finds some semiconducting and semimetallic materials and discovers several valuable materials,which provide help for the theoretical design and experimental synthesis of more novel two-dimensional multilayer magnets.