An exciting approach to theoretical spectroscopy

TL;DR

The paper surveys exciting, a comprehensive all-electron, full-potential package for theoretical spectroscopy, detailing its LAPW+LO basis, broad spectrum of ground- and excited-state methods (DFT, TDDFT, DFPT, GW, BSE, RIXS, pump–probe), and robust data/workflow infrastructure. It highlights recent methodological advances (mgga, DFT-1/2, hybrids, SVLO, cDFT, Wannier interpolation, scalable GW/BSE, non-equilibrium BSE, and exciton–phonon coupling) and demonstrates high precision across materials. The work emphasizes scalable HPC strategies, long-range interaction treatments, and non-equilibrium extensions, enabling accurate predictions of optical, X-ray, and pump–probe spectra. Moreover, it discusses an integrated software ecosystem with Python tooling, interfaces to SIRIUS and Cc4s, and NOMAD data infrastructure to support reproducible, data-driven spectroscopy. Overall, the paper positions exciting as a benchmark, extensible platform for cutting-edge theoretical spectroscopy with broad applicability to materials design and interpretation of complex spectroscopic experiments.

Abstract

Theoretical spectroscopy, and more generally, electronic-structure theory, are powerful concepts for describing the complex many-body interactions in materials. They comprise a variety of methods that can capture all aspects, from ground-state properties to lattice excitations to different types of light-matter interaction, including time-resolved variants. Modern electronic-structure codes implement either a few or several of these methods. Among them, exciting is an all-electron full-potential package that has a very rich portfolio of all levels of theory, with a particular focus on excitations. It implements the linearized augmented planewave plus local orbital basis, which is known as the gold standard for solving the Kohn-Sham equations of density-functional theory. Based on this, it also offers benchmark-quality results for a wide range of excited-state methods. In this review, we provide a comprehensive overview of the features implemented in exciting in recent years, accompanied by short summaries on the state of the art of the underlying methodologies. They comprise density-functional theory and time-dependent density-functional theory, density-functional perturbation theory for phonons and electron-phonon coupling, many-body perturbation theory in terms of the $GW$ approach and the Bethe-Salpeter equation. Moreover, we capture resonant inelastic x-ray scattering, pump-probe spectroscopy as well as exciton-phonon coupling. Finally, we cover workflows and a view on data and machine learning. All aspects are demonstrated with examples for scientific relevant materials.

Figures (26)

• Figure 1: Band gaps obtained with different metaGGA functionals. For comparison, PBE Uzulis2025, HSE06 Uzulis2025, and DFT-1/2 results are shown. All calculations were carried out with exciting.
• Figure 2: Convergence of the band gap $E_{\mathrm{gap}}$ of $\gamma$-CsPbI$_3$ with respect to the number of unoccupied states $N_{\mathrm{unocc}}$, comparing and . The gray shaded area indicates a tolerance window of $\pm 0.01\,\mathrm{eV}$ around the converged value
• Figure 3: Left: Band structure of diamond obtained using Wannier interpolation of eigenvalues from an $8^3$$\mathbf{k}$-grid using with the HSE functional. Right: as obtained from the original coarse grid (blue) and converged result obtained using Wannier interpolation on a grid of $100^3$ points (red).
• Figure 4: Electron-phonon coupling in MgB$_2$. Top: Phonon dispersion and mode resolved coupling strength $\lambda_{\nu\mathbf{q}}$ together with the phonon DOS (blue), the Eliashberg function $\alpha^2F$ (magenta), and the cumulative coupling strength $\lambda^{\rm cum}$ (dashed line). Bottom: Electron dispersion and band-resolved coupling strength $\lambda_{n\mathbf{k}}$ together with the electron DOS (blue) and coupling strength $\lambda$ (magenta).
• Figure 5: Electron-phonon coupling in diamond. Left: Direct (blue) and indirect (magenta) band gap $E_g(T)$ and its renormalization ${\Delta E_g(T) = E_g(T) - E_g^{\rm DFT}}$ as a function of temperature. Right: Band structure with the color code indicating the electron spectral function at 300.