arXiv subjects

Alexandre Cavalheiro Dias

Publications and source records attributed to Alexandre Cavalheiro Dias.

6 recordsLinked to original sources

arXiv2026

Engineering Excitons through Polymorphism and Dimensional Confinement in Low-Dimensional Tellurium

The interplay between dimensionality, band-edge electronic structure, and electron-hole interactions governs the optical response of low-dimensional tellurium, yet the microscopic origin of its excitonic behavior remains largely unexplored. Here, we investigate the quasiparticle, excitonic, and optical properties of two-dimensional tellurium polymorphs and one-dimensional helical nanowires using many-body GW and the Bethe--Salpeter equation. Our results reveal a strong dependence of the excitonic response on band-edge dispersion, crystal symmetry, and dimensional confinement. $α$-tellurene exhibits comparatively weak and spatially extended electron-hole correlations, whereas the SOC-induced quasi-flat band-edge states of $β$-tellurene give rise to a strongly bound and anisotropic near-infrared exciton. Momentum-resolved BSE eigenvectors and real-space exciton wave functions directly reveal the contrasting localization and anisotropy of these excitonic states. Remarkably, hydrogen-passivated hexagonal tellurene, previously identified as a quantum spin Hall phase with $Z_2=1$, supports an even larger direct exciton binding energy of 0.51 eV together with a compact and nearly isotropic in-plane excitonic distribution. This demonstrates that strong electron-hole correlations are fully compatible with nontrivial band topology, while the binding strength and spatial character of the exciton remain strongly dependent on the underlying band-edge electronic structure and crystal symmetry. The one-dimensional helical nanowire represents the strong-confinement limit, exhibiting a direct high exciton binding energy and a pronounced shift of the optical response toward the ultraviolet.

cond-mat.mtrl-sci↗

arXiv2026

Chemical Control of Electronic Structure and Topology in Tellurium-Encapsulated Silicene

We investigate chemical control of the electronic, optical, and topological properties of two-dimensional \ce{Si2X2Te2} (\ce{X} = \ce{B}, \ce{Al}, \ce{Ga}, and \ce{In}) monolayers using first-principles calculations. All compounds are dynamically stable semiconductors, with their vibrational and electronic properties evolving systematically upon group-III substitution. Hybrid-functional calculations including spin--orbit coupling reveal predominantly $p$-orbital band edges and increasingly pronounced relativistic effects from B to In. Most notably, the calculated $\mathbb{Z}_2$ invariant identifies \ce{Si2In2Te2} as a candidate quantum spin Hall insulator, while the B-, Al-, and Ga-based monolayers remain topologically trivial. Bethe--Salpeter calculations further show that electron--hole interactions redistribute oscillator strength near the absorption onset while preserving a weak in-plane optical anisotropy. Our results establish group-III substitution as a simple chemical route to tune the electronic structure and drive a transition from trivial to nontrivial topology in \ce{Si2X2Te2} monolayers.

cond-mat.mtrl-sci↗

arXiv2025

Teaching a Transformer to Think Like a Chemist: Predicting Nanocluster Stability

Atomically precise metal nanoclusters bridge the molecular and bulk regimes, but designing bimetallic motifs with targeted stability and reactivity remains challenging. Here we combine density functional theory (DFT) and physics-grounded predictive artificial intelligence to map the configurational landscape of 13-atom icosahedral nanoclusters X$_{12}$TM, with hosts X = (Ti, Zr, Hf), and Fe and a single transition--metal dopant spanning the 3$d$-5$d$ series. Spin-polarized DFT calculations on 240 bimetallic clusters reveal systematic trends in binding and formation energies, distortion penalties, effective coordination number, d-band centre, and HOMO-LUMO gap that govern the competition between core-shell (in) and surface-segregated (out) arrangements. We then pretrain a transformer architecture on a curated set of 2968 unary clusters from the Quantum Cluster Database and fine-tune it on bimetallic data to predict formation energies and in/out preference, achieving mean absolute errors of about $0.6-0.7$eV and calibrated uncertainty intervals. The resulting model rapidly adapts to an unseen Fe-host domain with only a handful of labelled examples. At the same time, attention patterns and Shapley attributions highlight size mismatch, $d$-electron count, and coordination environment as key descriptors. All data, code, and workflows follow FAIR/TRUE principles, enabling reproducible, interpretable screening of unexplored nanocluster chemistries for catalysis and energy conversion.

physics.chem-ph↗

arXiv2025

Flat bands in ultra-wide gap two-dimensional germanium dioxide

We employ first principles density-functional theory (DFT) and the Bethe-Salpeter equation (BSE) in the framework of tight-binding based maximally localized Wannier functions (MLWF-TB) model to investigate the electronic and optical properties of free-standing two-dimensional (2D) germanium dioxide phases. All investigated 2D GeO2 polymorphs exhibit ultra-wide band gaps and strong excitonic effects, with flat O-p-derived valence bands tunable under strain. These features allow the design of flat band materials with ultra large electronic gaps in low-dimensional systems, making these materials promising for devices operation at higher voltages and temperatures than conventional semiconductor materials.

cond-mat.mtrl-sci↗

arXiv2025

Electronic and optical and topological properties of defects in bismuthene

In this work we use first principles density-functional theory and Bethe-Salpeter equation together with tight-binding based maximally localized wannier functions (MLWF-TB) to investigate the electronic, optical and topological properties of two-dimensional bismuth (bismuthene) containing vacancy defects. We demonstrate that these properties depends on the shape and size of the nanopores. Furthermore, \textit{ab initio} molecular dynamics (AIMD) simulations shows that all pores are thermally stable at room temperature. Finally, adsorption of gas phase small molecules indicates that these pores can serve as sensors, opening the path for further applications in gas separation and sensing.

cond-mat.mtrl-sci↗

arXiv2025

Electronic and optical properties of two-dimensional flat band triphosphides

In this work we use first-principles density-functional theory (DFT) calculations combined with the maximally localized Wannier function tight binding Hamiltonian (MLWF-TB) and Bethe-Salpeter equation (BSE) formalism to investigate quasi-particle effects in 2D electronic and optical properties of triphosphide based two-dimensional materials XP$_3$ (X = Ga, Ge, As; In, Sn, Sb; Tl, Pb and Bi). We find that with exception of InP$_3$, all structures have indirect band gap. A noticeable feature is the appearance of flat valence bands associated to phosphorous atoms, mainly in InP$_3$ and GaP$_3$ structures. Furthermore, AIMD calculations show that 2D-XP$_3$ is stable at room temperature, with exception of TlP$_3$ monolayer, which shows a strong distortion yielding to a phase separation of the P and Tl layers. Finally, we show that monolayered XP$_3$ exhibits optical absorption with strong excitonic effects, thus revealing exciting features of these monolayered materials.

cond-mat.mtrl-sci↗