The coupling between electrons and phonons is at the heart of numerous physical phenomena and materials properties, from charge carrier transport to superconductivity and the temperature dependence of the electron energy bands and lifetimes to name a few [1]. Predicting and understanding these interactions is critical for the development of materials for new technologies, from optoelectronics to quantum technologies and spintronics. In recent years, there has been tremendous progress in the theoretical and computational modeling of electron-phonon interactions, driven by advances in first-principles theories, computational tools, and high-performance computing. It is time to bring together researchers working at the forefront of first-principles approaches to modeling electron-phonon processes in materials to discuss the state of the art, new ideas and developments from different codes, and some of the main open challenges.

Accurate and efficient calculations of electron-phonon coupling in bulk and reduced-dimensionality materials are now possible, thanks to refined interpolation techniques of the electron-phonon matrix elements [2,3,4,5] or efficient ab initio implementations of phonon-induced renormalization of band structures and phonon-assisted optical processes [6,7,8]. This allows, for example, for predictive first-principles calculations of phonon-limited carrier transport based on the Boltzmann transport equation formalism [9]. Important open challenges, however, involve computing high-field transport [10] and accounting for charge transport in the presence of polarons.

Polaron localization, when electrons, holes or other quasiparticles such as excitons become self-trapped due to the interaction with phonons, is a ubiquitous phenomenon that dramatically affects many materials properties [11]. The description of polarons from first-principles brings many challenges, and the development of new formalisms has shown the potential to discover exciting new physics [12].

Traditional ab initio approaches consider phonons as harmonic excitations within the adiabatic approximation. Taking into account phonon anharmonicity [13], non-adiabatic effects, and higher order vibronic couplings is crucial in materials such as ultrasoft perovskites or superconducting hydrides.

New theoretical methods and numerical implementations attempt to tackle also other aspects of electron-phonon physics, such as accounting for the effects of many-body electron correlations [14] and electron-phonon interactions out of equilibrium and in ultrafast dynamics [15,16]. Different approaches to treat exciton-phonon interactions within many-body perturbation theory [17,18,19], which are key to describing the behavior of many optoelectronic materials, aim to capture phenomena such exciton scattering rates, dissociation, and screening. However, the theoretical treatment of exciton-phonon coupling requires extensive computational resources, and even electron-phonon coupling for large systems is still prohibitive, especially using many-body methods. Innovative data-driven and machine learning approaches [20,21] may open the door to large-scale, ultrafast simulations of electron-phonon physics in realistic materials.

The workshop aims to bring together researchers with expertise in various areas of electron-phonon physics, focusing on developing new theories and computational methods. The goal is to discuss recent developments and new ideas as outlined above, associated challenges, and key open problems in this rapidly evolving area of research. We hope to stimulate discussions that will help push the boundaries of the theoretical description of key physics and materials applications influenced by electron-phonon interactions.