First-principles calculation of the bulk flexoelectric tensor

The first-principles theory of flexoelectricity has made impressive progress since the early pioneering works back in 2010. [R. Resta, PRL 105, 127601; J. Hong et al., JPCM 22, 112201] The main difficulty in dealing with the flexoelectric effect, i.e., the breakdown of translational symmetry, has been overcome since then by reformulating the problem in terms of long-wavelength acoustic phonons, within the framework of density-functional perturbation theory (DFPT). As of early 2020, a complete implementation of the bulk flexoelectric tensor is fully integrated in the latest release of the ABINIT package, which is now publicly available. Additional surface contributions have also been understood and can be accessed as a by-product of the main linear-response calculation. 

In this presentation, I will illustrate the underlying theoretical formalism of the implementation, which is based on an analytical long-wave extension of DFPT. I will also discuss the physical meaning of the bulk flexoelectric tensor as well as its individual components, and how to use them in order to build reliable models of experimentally observed phenomena.