We present a method to compute the electrooptic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. It allows us to study the non-linear optic behavior of three ferroelectric ABO_3 compounds : LiNbO_3, BaTiO_3 and PbTiO_3. Our calculations reveal the dominant contribution of the soft mode to the electrooptic coefficients in LiNbO_3 and BaTiO_3 and identify the coupling between the electric field and the polar atomic displacements along the B-O chains as the origin of the large electrooptic response in these compounds.
@article{arxiv.cond-mat/0311240,
title = {First-principles study of the electrooptic effect in ferroelectric oxides},
author = {Marek Veithen and Xavier Gonze and Philippe Ghosez},
journal= {arXiv preprint arXiv:cond-mat/0311240},
year = {2016}
}