All-functionals infrared and Raman spectroscopies, and their applications to materials design

Vibrational 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, the characterization of complex spectra frequently needs theoretical support in order to unambiguously decipher and assign the detected vibrational peaks. 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 vibrational 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. To demonstrate the capabilities of the approach and the need of modern exchange-correlation functionals, we first provide a conceptual illustration employing various (semi)local, Hubbard corrected, and hybrid functionals on the ferroelectric LiNbO₃ crystal, where we show that the best agreement with experiments is obtained with extended Hubbard or hybrid functionals. Second, we showcase the limitation of semi-local functionals in describing the Raman spectra of Li-ion phospo-olivine cathodes, and recover a good agreement with experiments when using self-consistent extended Hubbard corrections.