IMPURITY LEVELS AND NONLINEAR-OPTICAL PROPERTIES OF DOPED BATIO3 FROMEXTENDED CLUSTER LDA CALCULATIONS

The electronic structures of some transition-metal ions doping the fer roelectric oxide BaTiO3 are calculated through the density functional theory framework (LCAO-LSD ADF method) on extended clusters [XO,Ba,Ti, ] embedded in a punctual charge set depicting the crystalline environm ent. The transition ions X are Fe-n+(n = 2, 3, 4, 5), Ti3+, Nb4+, and Nb5+. Some related defects like Fe-V-o, where V-o stands for a lacunar oxygen site, are also investigated through a similar process. The pos itions of impurity levels insides the O-2p-Ti-3d band gap are obtained from eigenvalues and related optical transition or ionization energie s are calculated using excited states. This allows us to discuss the p hotorefractive effect present in such doped materials. The EPR fine-st ructure parameters a and D are also derived for Fe3+ in cubic and tetr agonal symmetries from crystal field calculations using parameters dra wn from molecular orbital results. (C) 1997 John Wiley & Sons, Inc.