Ab-initio study of active lone pair of Ge2+ cation in novel perovskite GeTiO3 compound

The effect of active lone pair Ge²⁺ in novel GeTiO₃ compound was investigated by ab-initio density functional theory (DFT) method as implemented in CASTEP computer code. In this work, the comparative of DFT study between novel GeTiO₃ compounds with lead-based PbTiO₃ compound have been carried out. From the calculation, we found that the corrected LSDA+U functional can improve and enhanced the electronic band gap of PbTiO₃ and GeTiO₃. The band structure shows a large band gap in GeTiO₃ with 2.09 eV at the optimized U = 2 eV. The analysis of density of states (DOS) revealed strong hybridization between O 2p - Ti 3d states with additional hybridization of Ge 6p states. The significant of the contribution active lone pair is demonstrated by Ge 4s states located at about 7 eV. It shows similarity to DOS of the PbTiO₃ compound where the active lone pair contributed the large ferroelectric polarization in PbTiO₃. The optical dielectric constants was also been investigated for further studies.