The First-principle Investigations And Quantum Chemistry Topology Analysis For Transition Metal Compounds

In one hand, the knowledge about bonding configuration of transition metal is an important part of the content of transition metal; in another hand, it is also importand in understanding other properties and mechanisms. However, the knowlege is still mostly based on the Octet rule. In the prsent work, the firt principle investigations and topology analyses combining Atoms in Molecules (AIM) theory with electron localization function (ELF) method were carried out for transition metal aluminides and cathode materials. Additionally, analyses on magnetic ordering in the cathode materials were also processed. The main contents are as follows:1. AIM analyses were performed for DO22- and L12-structure (Ti, V)Al3. The charges are accumulated at the bond critical point (BCP) of the Ti-Al bonds, V-Al bonds and Al-Al bonds and the interactions between the metal elements are pure shared-shell interactions. The metal bonds clearly haveπ-bond character.2. To better understand the formation mechanism of the pseudogap in the compounds (Ti, V)A13, the deformation charge density, band decomposed charge density, density of states and band structures were calculated. The crystal field eg-t2g split is the foundation of the pseudogap formation. Another important cause to induce the pseudogap is the inter-unit-cell orbital interaction, which broadens the gap in some range and narrows the gap in some other range.3. Six kinds of non-collinear Jahn-Teller distortion ordering models, i.e. the zigzag, dimer, windmill, trimer, altering trimer and honeycomb models, are built based on the non-distorted R3m structure for LiNiO2. The results of the GGA+U total energy calculations reveal that the zigzag structure is the most stable one and the collinear distorted C2/m structure is the next most stable one. Whereas, the Jahn-Teller distortion in the trimer, altering trimer and honeycomb models are endothermic.4. Six kinds of magnetic ordering patterns are built according to the crystal structure for NaNiO2 in C2/m structure. The GGA+U total energy calculations are performed for these patterns and it is found that the 3dx2-y2 electrons are also important in electron superexchange.5. GGA+U total energy calculations are also carried out for the magnetic patterns of LiMnO2 in C2/m structure. It is found that the inter-layer electron superexchange interactions are very weak and the CAF2/GAF2 is the ground magnetic structure. The analysis on the hopping paths deduced that the direct exchange interaction between manganese ions is the main motivity, which is much bigger than the Mn-O-Mn 90°superexchange interaction.6. Nine kinds of magnetic ordering patterns are built for LiMnO2 in Pmmn structure. The results of the GGA+U total energy calculation indicate the CAF3/GAF3 is the ground magnetic structure. The analysis on hopping paths suggests that the intra-layer Mn-Mn direct exchange interaction combined with the intra-layer Mn-O-Mn 180°superexchange interaction is the main motivity. The inter-layer Mn-Mn direct exchange interactions show frustration.7. In LiNiO2 and NaNiO2, the 3D deformation charge density distribution isosurfaces exhibit the difference in electron population between the Ni-3d orbitals and which is deduced by the oxygen octahedral crystal field eg-t2g split and further split on the two eg orbitals caused by Jahn-Teller distortion.8. AIM analysis was performed for the TM-0 bonds, which reveals that the BCP is nearer to the TM ions; charges are depleted and the local energy density are negative at the BCP, which indicate the transit closed shell interaction between the TM ions and the oxygen ion. The atomic basin populations indicate charge transfer from the TM ions to the oxygen ions. Therefore, the TM-0 bonds are dative bonds.9. The 3D ELF isosurfaces show that three equivalent bond localization domains around each oxygen ion exist in R3m structure for LiNiO2, whereas the bond basin of the short Ni-O bonds with low electron localization are overlapped by bond basin of the long Ni-O bond and lone pair basin of the oxygen ion with higher electron localization. In the bond basin the attractor locates in the oxygen atomic basin and most of the bond electrons populate in the oxygen atomic basin.10. There are bond basins not only of the long Ni-O bond, but also of the short Ni-O bonds in NaNiO2.11. In the monoclinic and orthorhombic LiMnO2, there are bond basins only of the short Mn-O bonds, whereas the bond basin of the long Mn-O bond is absent because of the oxygen lone pare basin nearby.