Refined Geometry and Frozen Phonons in KNbO3

TL;DR

This paper improves the accuracy of LMTO calculations for KNbO3 by optimizing basis choices and cutoffs, then investigates phonon instabilities and lattice dynamics using supercell frozen phonon methods.

Contribution

It provides a detailed analysis of basis and cutoff effects on off-center displacements and explores phonon instabilities in KNbO3 with optimized computational setup.

Findings

Optimized basis and cutoff choices enhance LMTO prediction stability.

Identified chain-structure instability in KNbO3.

Discussed the long-wavelength limit of LO phonons.

Abstract

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.