Molecular Magnets Nafe <sup> Ii </ Sup> <sub> 2 </ Sub> (po <sub> 4 </ Sub>) (hpo <sub> 4 </ Sub>), Magnetic And Electrical Conductivity Principle Study

In this thesis, first-principle calculations have been performed to study the electronic structure and the magnetic properties of non-pure organic magnet NaFe₂^Ⅱ(PO₄)(HPO₄). All calculations were performed using a full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT).To test the accuracy and precision of FP-LAPW method, the electronic structure and ferroelectric properties of the simple bulk BaTiO₃ were first studied. The analysis of the partial density of states indicates that Ti 3d states and O 2p states are greatly overlapped, showing strong hybridization between them. This orbital hybridization may lead to the spontaneous polarization in octahedron, and it results in aligned electric dipoles in bulk BaTiO₃, presenting ferroelectric property. External pressure and temperature can induce ferroelectric phase transition of BaTiO₃ because of changed orbital hybridization.For metal phosphonates NaFe₂^Ⅱ(PO₄)(HPO₄), a stable antiferromagnetic (AFM) ground state and a ferromagnetic (FM) metastable state were found in agreement with the experimental results. The calculated spin magnetic moment per molecule is 7.00μB, mainly from the FeⅡ. Density of states shows that NaFe₂^Ⅱ(PO₄)(HPO₄) is characteristic of semiconductor and conductor in AFM and FM states respectively. In order to further investigate the conductivity properties in FM and AFM states, we also give the electronic band structure, it is found that the bands have significant overlaps between the highest occupied molecule orbital (HOMO) and lowest unoccupied molecule orbital (LUMO) of spin-up and spin-down in FM states, while an energy gap of about 0.2eV in AFM states, based on this we can conclude that the FM metastable state has conductor properties, but AFM ground state has semiconductor properties.