Abstract
The density functional theory combined with the modern theory of polarization is used to understand themicroscopic origin of the piezoelectric effect in the hexagonal lithium iodate (alpha-phase). Calculations showthat the e33 and e14 piezoelectric-stress elements respectively have the highest and the smallest value inagreement with the experimental evidences. This e33 value is a consequence of the lone pair orbital of theIO3- group. Further insights are obtained by the separation of the piezoelectric-stress into a purely electronicand ionic contributions. The latter contribution has been also decomposed into contributions fromindividual atoms, as well as contributions from phonon normal modes. The full set of elastic constantswas computed, by means of which the piezoelectric-strain coefficients have been derived. These are discussedand compared to experimental data reported in literature.