Investigation of structural, electrical and magnetic properties of two dimensional transition metal dichalcogenides with density functional theory

In this thesis, the structural, electronic, and magnetic properties of two-dimensional transition metal dichalcogenides (TMDCs) have been comprehensively investigated using Density Functional Theory (DFT). It was determined that the properties of TMDCs, consisting of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Hf, Ta, and W) and chalcogen atoms (S, Se, and Te), significantly vary depending on their composition and their phases (hexagonal or trigonal). Structural analyses revealed that lattice constants, bond lengths, and interlayer distances change depending on the types of metal and chalcogen atoms. Electronic structure analyses showed that these materials exhibit semiconductor, metallic, and magnetic properties. Dynamic stability was evaluated using phonon band structures calculated with the finite displacement method. It was found that TMDCs in the hexagonal phase are generally dynamically stable, while more negative frequencies, indicating dynamic instability, were observed in trigonal phase compounds. Among the 84 TMDCs studied, 15 were identified as both dynamically stable and exhibiting magnetic properties. The magnetic properties of these compounds were analyzed using the 2D Ising model and Monte Carlo simulations. The results indicate that these materials are promising candidates for high-temperature applications, spintronic devices, and magnetic storage technologies. Additionally, the study examined the effect of the Hubbard parameter on the electronic and magnetic properties of two-dimensional TMDCs. In cases where the standard DFT method was insufficient, DFT+U corrections with the Hubbard parameter allowed for better accounting of the strong electron correlations in the d-orbitals of transition metals. The analyses revealed that the Hubbard parameter led to significant changes in the structural parameters, electronic structures, magnetic interactions, and Curie temperatures of the materials.