Investigation of physical properties of XPaO3 (X=Na, Rb and Cs) crystals with density functional theory

In this thesis, the structural, electronic and elastic properties of NaPaO3, RbPaO3 and CsPaO3 cubic crystals have been calculated theoretically using ABINIT software under Density Functional Theory. Firstly, volume optimisation was performed to find the theoretical lattice parameters of these crystals. Volume optimisation was calculated under both Generalized Gradient and Local Density approximations. The lattice parameter values obtained under both approximations gave very good results. All subsequent calculations were continued with the lattice parameters obtained under the Generalized Gradient approximation. The unit cells of these crystals were also plotted with the VESTA programme. In order to understand the electronic properties of NaPaO3, RbPaO3 and CsPaO3 crystals, electronic band graphs, total and partial density of state graphs were obtained for all these crystals. These crystals were found to be semiconductors. In order to reveal their elastic properties, elastic stiffness coefficients were first calculated. Then, using these values, Bulk, Shear and Young's moduli, Poisson's ratio, elasticity coefficient and Debye temperature expressions were calculated. It was revealed that these crystals are in elastic structure.