Automated all-functionals infrared and Raman spectra

TL;DR

This paper introduces an automated, open-source method for calculating infrared and Raman spectra from first principles, compatible with any functional and suitable for complex, low-symmetry materials, demonstrated on LiNbO3.

Contribution

The authors develop a versatile, user-friendly approach based on ground-state DFT and electric enthalpy functional for seamless spectra calculations with any functional.

Findings

Accurate spectra predicted for LiNbO3 using various functionals.

PBE0 and extended Hubbard functionals provide the best spectral matches.

Efficient sampling of the Brillouin zone with electric fields implemented.

Abstract

Infrared and Raman spectroscopies are ubiquitous techniques employed in many experimental laboratories, thanks to their fast and non-destructive nature able to capture materials' features as spectroscopic fingerprints. Nevertheless, these measurements frequently need theoretical support in order to unambiguously decipher and assign complex spectra. Linear-response theory provides an effective way to obtain the higher-order derivatives needed, but its applicability to modern exchange-correlation functionals remains limited. Here, we devise an automated, open-source, user-friendly approach based on ground-state density-functional theory and the electric enthalpy functional to allow seamless calculations of first-principles infrared and Raman spectra. By employing a finite-displacement and finite-field approach, we allow for the use of any functional, as well as an efficient treatment of large low-symmetry structures. Additionally, we propose a simple scheme for efficiently sampling the Brillouin zone with different electric fields. To demonstrate the capabilities of our approach, we provide illustrations using the ferroelectric LiNbO$_3$ crystal as a paradigmatic example. We predict infrared and Raman spectra using various (semi)local, Hubbard corrected, and hybrid functionals. Our results also show how PBE0 and extended Hubbard functionals yield in this case the best match in term of peak positions and intensities, respectively.