Electronic structure and optical response in Ca 4GdO(BO 3) 3 single crystals

Abstract

We have carried out ab initio calculations of band energy structure for gadolinium and calcium oxoborate (Ca 4GdO(BO 3) 3) (GdCOB). Both the ab initio norm-conserving pseudopotential (PP) and linear combination atomic orbital (LCAO) methods give essential disagreement with the experimental data first of all due to the presence of the highly localized 4d and 5f Gd states. Only the appropriate correction of the norm-conserving PP method by the orthogonalized LCAO wavefunctions essentially stabilizes the convergence procedure. To check the reliability of the proposed method we have carried out experimental investigations of the optical functions in the UV spectral range. Calculations were performed as a function of energy cut-off as well as of the Slater screening parameter x. The best agreement with the experiment can be achieved by using an orthogonalization procedure between the norm-conserving PP and LCAO wavefunctions. The last ones help in understanding the band electronic structure in the mentioned compounds. The possibility of achieving a good agreement between the experimental and theoretical optical imaginary part of the dielectric susceptibility data is shown.