Gamma phonons and microscopic structure of orthorhombic KNbO3 from first-principles calculations

TL;DR

This study uses first-principles calculations to analyze Gamma phonons and the microscopic structure of orthorhombic KNbO3, revealing detailed phonon properties and chain-like atomic arrangements.

Contribution

It provides a comprehensive first-principles analysis of Gamma phonons and the microscopic structure of orthorhombic KNbO3, including phonon frequencies, eigenvectors, and atomic displacement patterns.

Findings

Calculated phonon frequencies and eigenvectors for all Gamma modes.

Identified chain-like atomic displacement patterns in the orthorhombic phase.

Supported the existence of oppositely directed neighboring chains.

Abstract

{}From a series of total energy calculations by the full-potential linear muffin-tin orbital method, the total energy hypersurface as function of atomic displacements from equilibrium positions has been fitted for different Gamma phonon modes in orthorhombic KNbO3. Frequencies and eigenvectors of all TO Gamma phonons have been calculated in the harmonic approximation, and in the quantum oscillator scheme -- for A2 and B2 modes. The microscopic structure of the orthorhombic phase has been analyzed in a series of supercell calculations for different patterns of Nb displacements, providing indications in favour of the chain structure, with oppositely directed neighboring chains.