First-Principle Investigation On The Electronic Structure And Magnetic Properties Of New Functional Materials

In this thesis, the electronic structure of the partially filled tetrahedral semiconductors LiMgN, LiZnN, LiMgP, and the first silver palladium oxide Ag₂PdO₂ with a narrow band gap, and the electronic structure and magnetic properties of the trans-tetrachloro-bis-(pyridine)-rhenium organic compound were studied, using the full potential linearized augmented plane wave (FP-LAPW) and the full potential augmented plane wave + local orbital (FP-APW+lo) method within density functional theory. The partially filled tetrahedral semiconductors LiMgN and LiZnN can be viewed as the zinc-blende (MgN)^-and (ZnN)^-lattices partially filled with He-like Li⁺ ion interstitials. The conduction band distortions of LiMgN and LiZnN, compared to their corresponding zinc-blende AlN and GaN, are discussed. It was found that the insertion of Li⁺ ions at the interstitial sites near the cation or anion pushes the conduction band minimum of the X point in the Brillouin zone upward, relative to that of the Γpoint, for both (MgN)-and (ZnN)-lattices (the valence band maximum is at Γfor AlN, GaN, LiMgN, and LiZnN), which provides a method to convert a zinc-blende indirect gap semiconductor into a direct gap material, but the conduction band distortion of the βphase (Li+ near the cation) is quite stronger than that of the αphase (Li+ near the anion). The "interstitial insertion rule"cannot be applied in predicting all conduction band modifications. The total energy calculations show the αphase to be more stable than the βphase for both LiMgN and LiZnN. The Li-N and Mg-N bonds exhibit a strong ionic character, whereas the Zn-N bond has a strong covalent character in LiMgN and LiZnN. The conduction band modifications of LiMgP, compared to its corresponding zinc-blende AlP, are discussed. It was found that the conduction band valleys of LiMgP follow the X-Г-L ordering of increasing energy for both αand βphases, whereas AlP has the X-L-Гordering, and the differences between the direct (Г-Г) and indirect (Г-X) gaps decrease in the αand β-LiMgP, compared to AlP. The band calculations of LiMgP also show the interstitial insertion of closed-shell Li+ ion is a possible method to change the direct-indirect gap nature, but the "interstitial insertion rule"also couldn't predict all conduction band modifications of LiMgP, relative to AlP. The total energy calculations also show the αphase to be more stable than the βphase for LiMgP. The band structure calculations of Ag2PdO2 predicted that the compound has an indirect band gap, and the Pd 4d states strongly hybridize with the O 2p states all over the valence bands and conduction bands. The valence bands are composed mainly of Ag, Pd 4d states and O 2p states, while the conduction bands consist mainly of the Pd 4d states and O 2p states. In addition, focused on the calculation precision of the band gap, three different kinds of basis sets ("pure"LAPW, APW+lo and mixed LAPW/APW+lo) were chosen to calculate the band structure, the results show that the three basis sets lead to almost the same band gap values. The trans-tetrachloro-bis-(pyridine)-rhenium compound has the Re atom as the metallic magnetic center. The calculated total energies revealed that the compound has a stable antiferromagnetic ground state, which is in agreement with the experiment. The calculated magnetic moment per molecule is 3.00 μB, the magnetic moments are mainly from the Re atoms with a 5d3 electronic configuration. The antiferromagnetic interaction between ferromagnetically coupled Re atom layers passes through the p orbitals of the Cl ligands near Re atoms.