Lattice dynamics of wurtzite-type crystals including the effect of the electronic extension

Birman has given a physical meaning to the Ewald method and has given a potential including the effect of the electronic extension with the use of this method. Thus we can easily take into account the effect of the electronic extension with the use of the Birman method without considering any other new procedures. On the basis of the polarizable-ion model, after applying the Birman method we have calculated macroscopic quantities (wave number, elastic constant, and piezoelectric constant), and examined the contribution of this effect to them. The result is that the effect is not so small that it can be neglected, and enables better agreement with the observed macroscopic quantities to be obtained.