Structural, electronic and elastic properties of KCaF_3 and RbCaF_3 for vacuum-ultraviolet-transparent lens materials

摘要

The first principles calculation within the full potential linearized augmented plane wave (FP-LAPW) method is applied to study the structural, electronic and elastic properties of cubic perovskite-type compounds KCaF_3 and RbCaF_3. The exchange correlation effects are included through the LDA, GGA and modified Becke-Johnson (mBJ) exchange potential. The calculated structural properties such as equilibrium lattice constant, the bulk modulus and its pressure derivative are in good agreement with the available data. KCaF_3 and RbCaF_3 have wide and indirect band gaps and they agree with experimental values. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young's modulus and Poisson's ratio are obtained for the first time. KCaF_3 and RbCaF_3 are elastically anisotropic and the B/G ratio indicate that these are ductile materials.