Paper Title
Study And Characterization Of Xcaf3 (X = K And Rb) Compounds

Abstract
The wide band gap of the alkaline earth fluorides lets them to be prospective candidates for vacuum-ultraviolet-transparent lenses used in optical lithography steppers and to be promising for fast scintillators. The KCaF3 and RbCaF3have been characterized usingthe plane wave pseudo-potential method within density functional theory (DFT). We investigatedthe structural, elastic, electronic and optical properties of XCaF3 (X = K and Rb) insulating. The studied compounds show a weak resistance to shear deformation compared to the resistance to the unidirectional compression. KCaF3 and RbCaF3 are considered ductile. The elastic constants and related parameters were predicted. The stiffness is more important in KCaF3, whereas, the lateral expansion is more important in RbCaF3. KCaF3 and RbCaF3 have R-  indirect band gap. The main peaks in the imaginary part of the dielectric function correspond to the transition from the occupied state F-p to the unoccupied states Ca: s or K, Rb: p. At lower energies, KCaF3 and RbCaF3 show the same optical properties. Under pressure effect, the peaks of imaginary part of dielectric function were shifted toward high energy. Keywords�The alkaline earth fluorides, DFT, Ab initio calculations, Properties.