We model the ferroelectric and paraelectric phases in the YMnO3 and YMn2O5, compounds with discussion of the hyperfine parameters at the atomic nuclei: electric field gradient and magnetic hyperfine field, using first-principles density functional theory FP-L/APW+lo method (WIEN2K code). The differences of the changes in hyperfine properties and their correlation due to the onset of polarization in both cases reveal their sensitivity to the different electronic densities changes due to

more »

... tricity. In the case of YMnO3 the greater changes appear in the Y and O atoms, while in YMn2O5, where the polarization is induced by a magnetic transition, the parameters at Mn and its bonded O atoms are changed the most. The sensitivity of the parameters to different degrees of approximation in calculations is also discussed.