Quantum paraelectricity in the self-consistent phonon approximation

The dielectric susceptibility of potassium tantalate has been computed in t he framework of an approach, earlier proposed by Vaks [V.G. Vaks. Vvedenie v mikroskopicheskuiu teoriju segnetoelektrikov. Moskva, Nauka 1973 (in Russ ian)]. This theory deals with a perturbation series for the temperature Gre en functions rather than with the mean field approach. The small parameter is the anharmonicity potential. The phonon spectrum, required for the compu tation, was taken from a recent study by Farhi et. al. [Europ. Phys. J. B ( in print)]. Qualitative agreement has been obtained between theory and expe riment.