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

A new method for calculation of electronic structure for LiNbO3-Nd,MgO was proposed. Our approach is based on molecular dynamics simulation and quantu m chemical calculations. The crystalline structure is presented as a superp osition of ideal translational lattices. Dopants are considered as modulati on centers taken with appropriating weighting factors. We have found that t he 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 possi ble structural configurations were also taken into account. From the ab ini tio 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 componen t. Role of the particular structural fragments effectively contributing to the electrooptic coefficient is clarified. We have compared theoretically c alculated values with the experimental data with the different Nd and Mg co ntents. Essential role of the electron-phonon contributions in the observed dependencies have been revealed.