Research

Time-dependent many-body effects in materials for photovoltaics

With Lucia Reining and Lionel Lacombe we develop a response-theory framework for electron charge dynamics and charge separation that can be evaluated efficiently on realistic materials.

Designing better photovoltaic absorbers requires accurate, predictive descriptions of dielectric properties, exciton binding energies, and band offsets at interfaces — quantities where mean-field approaches routinely fail. Through the PEPR TASE project MINOTAURE and the Energy4Climate center, my group studies hybrid perovskites and other emerging absorbers from first principles.

Key papers: SciPost Phys. 20, 035 (2026); Small (2026): e11410.

Excitons, screening, and the optical properties of complex oxides

Optical absorption and electron energy loss spectra are governed by the interplay between single-particle excitations and the screening of the Coulomb interaction by the electron cloud. In flat-band materials like V₂O₅, the simple Frenkel picture of localised excitons breaks down: localised charge-transfer excitations combine to form strongly bound excitons that nevertheless extend over large electron–hole distances, with anisotropy controlled by the local crystal structure.

We've shown that dark excitons with even larger binding energy accompany the bright ones, and that local distortions — for instance along phonon modes — modify the screening in ways that propagate cleanly through EELS and absorption. These structure–properties relations matter for using V₂O₅ as an energy-storage material, and the framework generalises to other complex oxides.

Key papers: npj Comput. Mater. 8, 94 (2022); Phys. Rev. B 107, 075101 (2023).

Quantum Monte Carlo for excited states and one-body observables

QMC offers a path to accurate many-body energies, but extending it to spectroscopic observables — quasiparticle excitations, optical gaps, reduced density matrices — is an active methodological challenge. I work on QMC algorithms that compute electronic excitation spectra and one-body reduced density matrices directly, and on benchmarking the resulting predictions against MBPT (GW, Bethe–Salpeter) for systems where both approaches can be brought to bear.

Recent applications include molecular hydrogen in Phase I — where we combined QMC with MBPT to predict excitation spectra — and the neutral band gap of diamond, where QMC provides a benchmark for approximate functionals.

Key papers: Phys. Rev. B 109, L241111 (2024); Condens. Matter Phys. 26, 3 (2023).

Dense hydrogen at extreme conditions

Hydrogen under planetary-interior pressures remains one of the most fundamental problems in condensed matter — and one of the most demanding benchmarks for electronic-structure theory. My PhD work, continued in collaboration with David Ceperley, Markus Holzmann, and Carlo Pierleoni, used coupled electron-ion Monte Carlo and MBPT to study the electronic structure of molecular hydrogen across its solid phases, including optical and quasiparticle gaps in Phase I.

PhD thesis (2020): Quantum Monte Carlo methods for electronic structure calculations: application to hydrogen at extreme conditions.