  In order to arrive at ultimately accurate results available with the LMTO
method in the local density approximation, the stability of full-potential LMTO
predictions for off-center displacements in KNbO3, as depending on the choice
of basis and expansion cutoffs, has been thoroughly investigated. With the
calculation setup thus optimized, supercell frozen phonon calculations aimed at
the study of the chain-structure instability over the Brillouin zone have been
done, and the long-wavelength limit of the LO phonon is discussed.
