Study Of Electronic Structure And Magnetism Of Chromium Nitride With NMTO Method

Due to the rapid development of computer science, the first-principle calculation method based on density functional theory becomes a powerful tool and plays an important role in material, physics, chemistry and biology. Recently developed tight-binding linear muffin-tin orbital (LMTO) and N-order muffin-tin orbital (NMTO) methods with the downfolding technique are two efficient schemes which provide quite high precise and save much computing time.Recent years, nitrides attract much attention due to its excellent resistant of corrosion and oxidation in surface engineering technique. CrN can be easily fabricated, which has good thermal stability and resistance of corrosion. Furthermore, it applies not only to surface preservative but also in high temperature friction, such as cutting, micro-drill bit and engine-piston, etc. However, its fundamental physical properties are still not completely understood, especially the phenomenon at low temperature, such as structural transition, magnetic transition and insulator-metal transition, which caused by complex interplay between electron, spin and lattice.In this thesis, we have investigated the electronic structure, structural and magnetic properties of chromium nitride by employing both LMTO and NMTO methods. We have investigated the electronic structure of both the cubic and orthorhombic structure CrN, and obtained the parameters for TB Hamiltonian with downfolded Cr d orbitals including both t2g and eg orbitals. Furthermore, the chemical bonding, electronic properties, magnetism and the distortional effect are analyzed according to the TB parameters.Our calculation confirms that ferromagnetic states found in experiment are ground states and the total energy only changes very tiny when the lattice of CrN distorts from the original cubic Fm3m to the orthorhombic Pnma phase. The electronic structure calculations reveal that the five nearest hopping integrals should be taken into account. It is also found that the lattice distorts primarily affect the hopping integrals on the xy plane. Our results indicate that the first-NN hopping integral txz,yz and t3Z2-1,xy should be responsible for the effect of orthorhombic distortion and the long range hopping terms have little contribution. Our results might be helpful for the further investigation to consider the complex strong correlation effect in the compound.