  Density Functional Theory (DFT) calculations were used to evaluate polarity
of group III nitrides, such as aluminum nitride (AlN), gallium nitride (GaN)
and indium nitride (InN) providing physically sound quantitative measure of
polarity of these materials. Two different approaches to polarization of
nitride semiconductors were assessed and the conclusions have been used to
develop models. It was shown that Berry phase formulation of the electron
related polarization component provides a number of various solutions,
different for various selection of the simulated volume. The electronic part
gives saw-like pattern for polarization. A total number of these solutions,
related to well known scaling of the geometric phase, is equal to the number of
valence electrons in the system. Summation with similar pattern for ionic part
provides several polarization values. Standard dipole density formulation
depends on the selection of the simulation volume in periodic continuous way.
Using a condition of continuous embedding into the infinite medium, and
simultaneously, the zero surface charge representation at crystal boundary
provides to physically sound solution. This solution is corresponding to
maximal and minimal polarization values and also corresponds to different
physical termination of the crystal surfaces, either bare or covered by
complementary atoms. This change leads to polarization and electric field
reversal. The polarization and related fields in finite size systems were
obtained.
