Massimiliano Stengel
(ICREA, Spain)

Abstract:
 
Flexoelectricity, describing the polarization response to a gradient of the strain, is a universal property of all insulators that has attracted considerable attention in the past few years. In spite of its fundamental and practical interest, it has long resisted theoretical attempts at quantifying it with predictive accuracy in realistic materials. In this talk, I will introduce the methodological advances that have recently lifted this limitation in the context of first-principles theory. I will emphasize the generality of these newly established theoretical tools, whose applicability goes well beyond the specifics of flexoelectricity. Examples of spatial dispersion effects that can now be calculated with minimal effort include natural optical activity, generalized Lorentz forces and dynamical quadrupoles.
 
In the second part of my talk, I will discuss some general issues related to the treatment of long-range interactions in the long-wavelength limit. Macroscopic electrostatic and elastic fields have a nonanalytic behavior at small wavevectors, which generally leads to ambiguities in the definition of the spatial dispersion coefficients. This calls for extra care when incorporating the calculated materials parameters into macroscopic models: one must make sure that the overall theory yields unique physical answers even if the individual terms are ill-defined as stand-alone properties. I will give special focus to the two-dimensional (2D) case, and on the proper representation of the leading electrostatic and electromechanical couplings therein.

Zoom registration link will soon follow.

Coffee/Tea Refreshments
will be served prior to the Seminar
at 10:30 in the Leonardo Building Bar