Polarization properties of ZnO and BeO: Anab initiostudy through the Berry phase and Wannier functions approaches

The spontaneous polarization and the piezoelectric constants of ZnO and BeO are calculated at an ab initio quantum-mechanical level by using two alternative strategies, namely, through the Berry phase scheme applied to delocalized crystalline orbitals, and through the definition of well-localized Wannier functions. The two sets of results, obtained in the same computational conditions (both schemes are implemented in the CRYSTAL code) compare extremely well, and are in good agreement with available experimental data.