Public thesis defense Viet-Anh TRAN - IMCN
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Computational Modeling of the Electronic and Vibrational Properties of Twisted Two-Dimensional Materials
Thursday October 29th, 2026 - 4:15pm - Auditorium SUD03 - Place Croix du Sud, 1 - 1348 Louvain-la-Neuve
Van der Waals heterostructures, assembled from atomically thin crystals, offer a way to tune material properties beyond chemical composition. When two layers are stacked with a small twist angle or a slight lattice mismatch, a moiré superlattice forms with a period much larger than the interatomic distance. The resulting modulation of the local stacking reshapes the electronic and vibrational properties of the system, which can change markedly with small variations in orientation, interlayer spacing, or stacking energy. Describing these effects at the atomistic scale requires tools that are both accurate and efficient, since first-principles methods alone are too costly for the large cells involved.
This thesis addresses three aspects of this problem. First, it studies electronic transport in graphene on hexagonal boron nitride (h-BN), where the misalignment angle between the two lattices controls the interplay between Klein tunneling and Fabry-Pérot interference through moiré-induced sublattice symmetry breaking. Second, it develops machine-learned interatomic potentials for twisted bilayers. Broadly trained foundation models are found not to reliably resolve the interlayer energetics that govern atomic reconstruction, and a fine-tuning workflow is established that reaches near-first-principles accuracy for graphene, h-BN, and MoS₂. Third, the validated potential is applied to twisted bilayer graphene under hydrostatic pressure and compared with Raman measurements. The folding of out-of-plane and in-plane phonon branches by the moiré superlattice is discussed as a possible origin of narrow, pressure-dependent Raman peaks observed experimentally.
Together, these results clarify how twist angle, substrate coupling, and pressure modify the properties of moiré systems, and provide computational tools to study them at the atomistic scale.
Jury members
Prof. Jean-Christophe Charlier (UCLouvain), Supervisor
Prof. Xavier Gonze (UCLouvain), Chairperson
Prof. Gian-Marco Rignanese (UCLouvain), Secretary
Dr. Viet-Hung Nguyen (UCLouvain)
Prof. Luc Henrard (UNamur)
Dr. Sylvain Latil (CEA Saclay, France)