Influence of Nd:MgO dopants on the electrooptical effect in LiNbO3 single crystals

A new method for calculation of electronic structure for LiNbO 3 -Nd,MgO was proposed. Our approach is based on molecular dynamics simulation and quantum chemical calculations. The crystalline structure is presented as a superposition of ideal translational lattices. Dopants are considered as modulation centers taken with appropriating weighting factors. We have found that the more probable are two types of local dopants. The first one corresponds to the Mg Nb configuration and the second to the Nd Li centers. Other possible structural configurations were also taken into account. From the ab initio norm-conserving pseudopotential (PP) calculations modified by the LCAO quasi-core states we have calculated electronic part of electrooptic tensor component r 222 tensor component. Simultaneously we have evaluated phonon and electron-phonon anharmonic contributions to the r 222 tensor component. Role of the particular structural fragments effectively contributing to the electrooptic coefficient is clarified. We have compared theoretically calculated values with the experimental data with the different Nd and Mg contents. Essential role of the electron-phonon contributions in the observed dependencies have been revealed.