First-Principles Modeling of Nonlinear Interactions in Materials

In the 1990’s, first-principles-based methods began to be commonly used and/or developed to investigate simple ferroelectrics such as BaTiO3 or PbTiO3. Since then, these schemes have been generalized to understand much more complex systems and phenomena and even to predict striking features that were then experimentally confirmed. However, several current issues in the world of ferroelectrics would still require the development of novel ab-initio schemes to gain a deeper insight into them. This includes some aspects of electro-optic (EO) and elasto-optic conversions, that characterize the change of refractive index under an applied electric field and strain, respectively. In particular, the computations of (linear and quadratic) electro-optic conversion and elasto-optic responses at finite temperature, in low-dimensional systems, and/or in the THz regime are missing to understand puzzling measurements (see, e.g., Ref. [1] that reports a linear electro-optic response in BaTiO3 while Ref. [2] measured a quadratic EO conversion in the same material).

The aim of this Talk is to discuss the recent development and use of several novel first-principles-based approaches that allow to tackle all these issues, providing an unprecedented insight into them along with new predictions to be experimentally checked [3-6].