Born effective charges, dielectric constants, and lattice dynamics of KNbO sub(3)

We performed first principles LAPW linear response calculations for KNbO sub(3) in the cubic, experimental tetragonal, and theoretical ground state rhombohedral structures. We found that the Born effective charges and dielectric constants strongly depend on the small atomic displacements involved in the ferroelectric phase transitions. We also calculated the zone center phonons for the cubic structure and compared them with previous LDA results.