Nonempirical calculation of structural and dynamic properties for KZnF3 and K2ZnF4

Nonempirical interionic potentials were used to calculate structural properties (lattice constant, ion positions in the unit cell, elastic and dielectric constants) and dynamic properties (vibration dispersion curves) for KZnF 3 and K 2 ZnF 4 crystals, which consist of the same ions but have different crystal structures. Anomalous pressure dependences of the rotational mode frequencies were found; these are unstable in the perovskite and two-dimensional perovskite lattices