Ab initiostudy of the spontaneous polarization of pyroelectric BeO

The spontaneous bulk polarization of wurtzite BeO is studied using ground-state first-principles theory. This quantity, which is not accessible when imposing periodic boundary conditions, is obtained with a novel approach based on the supercell method. The calculated macroscopic polarization is ${\mathit{P}}_3$=1.5×${10}^{\mathrm{-}2}$ C/${\mathrm{m}}^2$, and mostly results from the internal crystallographic distortion. No experimental value of ${\mathit{P}}_3$ exists, but the calculated differences in polarization, between different geometries, compare well with available data.