A theoretical study of fluorides scintillating crystals: Methodology and application

Theoretical computation and simulation study has been performed on important scintillating fluorides crystal BaF₂ and PbF₂. The structural, electronic, transport and defects properties are investigated under different methodology schemes. The thesis provide accurate and detailed understandings of fundamental electronic structures of them in different phases for the very first time. A new expanded module for which provide the CRYSTAL program package with full capability in ECP (effective pseudo-potential) method calculation is developed and successfully applied into the this study.; We present the results of an all-electron first principles study on BaF ₂ in its stable (cubic) and high-pressure phases. A LCAO (linear combination of atomic orbitals) approach in the framework of DFT is employed for total energy calculations in cubic, orthorhombic and hexagonal phases of BaF ₂. A fitting of the energy surface to the equation of state yields the lattice constant and the bulk modulus of these phases at zero pressure which are in good agreement with the corresponding experimental values. Analysis of band structure determines the high-pressure phases to be direct-gap materials and no metallization of BaF₂ is predicted to occur for pressures up to 50 GPa. Furthermore, several peaks observed in the spectroscopic experiments have been identified with interband transitions in the cubic BaF₂.; We also performed the small-core ECP first principles calculation on Pb₂ in its cubic, orthorhombic and hexagonal phases. For cubic phase, the accurate theoretical band data now are available with the structural properties were very well generated. It is predicted with direct band gap at X. The band structures of orthorhombic and hexagonal phases are first time calculated. We predict the orthorhombic and hexagonal phase PbF₂ has indirect band gap. These results may help to clarify some doubts and controversies in the experiments and promote the application studies.; At last, a discussion on the results from this study is held. Special attention is paid to the methodology level questions on theoretical computations and simulations. The main limitations of methods used in this work are summarized and analyzed with future method developments and application studies suggested. The thesis finally concludes with some fundamental perspectives in theoretical computation and simulation work. (Abstract shortened by UMI.)...