Stability and phonons ofKTaO3

${\mathrm{KTaO}}_3$ was investigated using density functional methods. These local-density approximation calculations correctly show the absence of a ferroelectric instability in this compound. Phonon frequencies and bulk properties in good agreement with existing measurements are obtained. A highly anharmonic low-frequency mode corresponding to the observed incipient ferroelectric behavior is identified. The electronic structure shows strong transition metal oxygen covalency as in known ferroelectric perovskites. As expected properties show a strong similarity with ${\mathrm{KNbO}}_3$. The absence of ferroelectricity in ${\mathrm{KTaO}}_3$ is due to the extreme sensitivity of the soft mode to the covalency and the slight chemical differences of Nb and Ta, particularly the higher d binding energy in Nb.