IESL SEMINAR
Wednesday 27/08/2025, 12:00
FORTH Seminar Room: C. Fotakis
Title:Computational Characterization of Metallic and Semiconducting Materials via Many-Body
Perturbation Theory
Abstract:
The accurate prediction of optical and excitonic properties in low-dimensional materials
presents a unique set of theoretical and computational challenges—particularly when dealing
with the competing electronic characteristics of semiconducting and metallic systems. In this
talk, I present a set of diverse, yet interconnected studies conducted using first-principles
calculations within the framework of Many-Body Perturbation Theory (MBPT).
For semiconducting transition metal dichalcogenides (TMDs), we investigate the influence of
external electric fields and strain on the excitonic landscape in bilayer WSe₂. We reveal how
stacking-dependent interlayer hybridization governs nonlinear Stark shifts and spectral
symmetry-breaking, explaining recent experimental anomalies. In Janus-based TMD
heterostructures, we demonstrate how intrinsic dipolar fields modify band alignments and
enhance phonon-mediated generation of interlayer excitons, highlighting the role of exciton
phonon coupling in carrier separation.
Turning to metallic layered systems, we address the longstanding challenge of optical
characterization in MXenes. By carefully incorporating intraband transitions, we show that
while GW corrections significantly alter the band structure, sometimes even producing pseudο-gapped features, excitonic effects remain minimal, validating the use of the independent
particle approximation (IPA) for optical property prediction in this class. Finally, in vanadium
dioxide (VO₂), a temperature-driven phase transition material, we capture both the strong
excitonic effects in the insulating monoclinic phase and the reliable RPA-level response in the
metallic rutile phase, achieving excellent agreement with experimental spectra across regimes.
Drawing on these results, I will reflect on the advantages, limitations, and subtleties
encountered in our extensive experience applying first principles level Many Body Perturbation
theory across this broad materials landscape—illustrating what makes computational many
body theory both fruitful and, at times, challenging.