BORN EFFECTIVE CHARGES, DIELECTRIC-CONSTANTS, AND LATTICE-DYNAMICS OFKNBO3

We performed first principles LAPW linear response calculations for KN bO3 in the cubic, experimental tetragonal, and theoretical ground stat e rhombohedral structures. We found that the Born effective charges an d dielectric constants strongly depend on the small atomic displacemen ts involved in the ferroelectric phase transitions. We also calculated the zone center phonons for the cubic structure and compared them wit h previous LDA results.