Electronic structure and optical response in Ca4GdO(BO3)(3) single crystals

We have carried out ab initio calculations of band energy structure for gad olinium and calcium oxoborate (Ca4GdO(BO3)(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. On ly the appropriate correction of the norm-conserving PP method by the ortho gonalized LCAO wavefunctions essentially stabilizes the convergence procedu re. To check the reliability of the proposed method we have carried out exp erimental 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 ca n be achieved by using an orthogonalization procedure between the norm-cons erving PP and LCAO wavefunctions. The last ones help in understanding the b and electronic structure in the mentioned compounds. The possibility of ach ieving a good agreement between the experimental and theoretical optical im aginary part of the dielectric susceptibility data is shown. (C) 1999 Elsev ier Science B.V. All rights reserved.