Ultra-Wide Bandgap (UWBG) semiconductor materials, particularly cubic boron nitride (c-BN), are emerging as critical components in high-power and high-temperature electronic applications due to their exceptional properties. These properties include high thermal stability, high breakdown voltage, and significant thermal conductivity, making c-BN a promising candidate for effective thermal management in advanced electronic devices such as high-performance transistors and power electronics. However, challenges remain in optimizing thermal transport mechanisms within these materials, highlighting the need for a deeper theoretical understanding to enhance device performance. This project aims to theoretically investigate the thermal conductivity of c-BN and other UWBG materials using a combination of density functional theory (DFT) and the phonon Boltzmann transport equation (BTE). The specific objectives of the project are to: 1. Understand the effects of tensile strain on the thermal conductivity of c-BN. 2. Investigate the effects of defects and interfaces in c-BN. 3. Examine how tensile strain and defects affect the thermal conductivity of other UWBG materials, such as GaN, AlN, and ternary alloys like AlₓGa₁₋ₓN, which also show promise for high-power and high-temperature applications. We will begin our investigation with ab initio calculations to optimize the lattice structure of c-BN (considering both strain and defects) and perform self-consistent field calculations to determine the interatomic force constants critical for subsequent thermal analysis. After obtaining these force constants via DFT, we will employ phonon BTE to perform comprehensive thermal calculations, including phonon dispersion, the phonon density of states (PDOS), phonon mean free path (MFP), relaxation times, group velocities, and specific heat. These calculations will employ the relaxation time approximation (RTA) to estimate thermal conductivity at a range of temperatures.