First-principles study of lattice dynamical properties of the room-temperature $P2_1/n$ and ground-state $P2_1/c$ phases of WO$_3$

TL;DR

This study uses first-principles density functional theory to analyze the lattice dynamical properties of WO$_3$'s room-temperature and ground-state phases, providing detailed phonon spectra and insights into phase stability and structural features.

Contribution

It offers a comprehensive theoretical analysis of WO$_3$'s dynamical properties, validating computational methods and linking spectral features to structural distortions.

Findings

Both phases are dynamically stable based on phonon dispersion curves.

The Raman spectrum peaks correlate with antipolar distortions in the structure.

Hybrid functionals like B1-WC provide the best description of WO$_3$ properties.

Abstract

Using first-principles density functional theory, we investigate the dynamical properties of the room-temperature $P2_1/n$ and ground-state $P2_1/c$ phases of WO$_3$. As a preliminary step, we assess the validity of various standard and hybrid functionals, concluding that the best description is achieved with the B1-WC hybrid functional while a reliable description can also be provided using the standard LDA functional. We also carefully rediscuss the structure and energetics of all experimentally observed and a few hypothetical metastable phases in order to provide deeper insight into the unusual phase diagram of WO$_3$. Then, we provide a comprehensive theoretical study of the lattice dynamical properties of the $P2_1/n$ and $P2_1/c$ phases, reporting zone-center phonons, infrared and Raman spectra as well as the full phonon dispersion curves, which attest for the dynamical stability of both phases. We carefully discuss the spectra, explaining the physical origin of their main features and evolution from one phase to another. We reveal a systematic connection between the dynamical and structural properties of WO$_3$, highlighting that the number of peaks in the high-frequency range of the Raman spectrum appears as a fingerprint of the number of antipolar distortions that are present in the structure and a practical way to discriminate between the different phases.