arXiv subjects

Andreia Luisa da Rosa

Publications and source records attributed to Andreia Luisa da Rosa.

14 recordsLinked to original sources

arXiv2026

Transition-Metal Chalcogenide Nanowires: A First-Principles Study of Stability, Electronic Structure, and Mechanical Response

Subnanometer transition-metal chalcogenide nanowires provide a one-dimensional platform in which electronic functionality and mechanical response can be tuned through chemical composition. Here, density functional theory calculations are combined with machine-learning force-field (MLFF) molecular dynamics to investigate MoS, MoSe, MoTe, WS, WSe, and WTe nanowires. The optimized structures are dynamically stable within the harmonic approximation, and their electronic character evolves systematically across the chalcogen series: MoS, MoSe, WS, and WSe are metallic, whereas MoTe and WTe are semiconducting, with HSE06 band gaps of 0.52 and 0.20 eV, respectively. The effective axial stiffness decreases from sulfides to selenides and tellurides, consistent with the increase in metal--chalcogen bond length; using a circular effective cross section, the corresponding Young moduli range from 392 to 718 GPa. All six nanowires have negative formation energies relative to the selected elemental reference phases. MLFF trajectories extending to 2.5 ns at 300 K preserve the one-dimensional morphology and local atomic order, providing evidence of finite-temperature dynamical stability on the simulated time scale. The corresponding MLFF molecular-dynamics energy traces are shown in. We further examine the response of the nanowires to axial strain and curvature, including strain-induced band-gap modulation in the tellurides. These results establish composition and mechanical deformation as complementary routes for tuning the electronic and mechanical properties of ultrathin transition-metal chalcogenide nanowires and support their further investigation as components of flexible nanoelectronic systems.

cond-mat.mtrl-sci↗

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↗

arXiv2026

First-principles calculation of electronic and topological properties of low-dimensional tellurium

We present a comprehensive first-principles investigation of the structural, electronic, vibrational, and topological properties of tellurium across its dimensional hierarchy, including bulk trigonal Te-I, two-dimensional tellurene polymorphs, and one-dimensional helical nanowires. Using density functional theory with full inclusion of spin-orbit coupling, we confirm that bulk Te-I is a narrow-gap semiconductor hosting Weyl nodes arising from broken inversion symmetry and degenerate phonon modes suggestive of chiral phonon behavior. In contrast, two-dimensional alpha and beta-tellurene are found to be topologically trivial, with no spin-orbit-driven band inversion in the occupied manifold. Beyond these established phases, we find that buckled kagome and buckled square tellurene lattices exhibit a nontrivial two-dimensional topology of the occupied electronic bands, indicating incipient quantum spin Hall character in metallic systems. In contrast, one-side hydrogen-passivated hexagonal tellurene realizes a fully gapped quantum spin Hall phase with a robust Z2 = 1 invariant, preserved under applied strain and chemical functionalization. In the one-dimensional limit, helical tellurium nanowires preserve chirality and host edge-localized states accompanied by pronounced anisotropy in carrier effective masses. These results establish tellurium as a highly tunable platform for engineering topological phenomena across dimensionality, bridging three-dimensional Weyl physics, two-dimensional quantum spin Hall and incipient Z2 phases, and one-dimensional helical systems.

cond-mat.mtrl-sci↗

arXiv2026

Hydrogen storage in pristine and Janus transition-metal dichalcogenide monolayers: electronic origins, coverage effects, and finite-temperature stability

Here, we present a systematic first-principles study of hydrogen adsorption on pristine and Janus MX2 and MSSe monolayers (M = Ni, Pd, Pt; X = S, Se), combining density-functional theory (DFT) calculations with finite-temperature ab initio molecular dynamics simulations (AIMD). Orbital-resolved electronic-structure analysis reveals that hydrogen binding strength is controlled primarily by the contribution of metal d states near the Fermi level, which increases from Pd and Pt to Ni. Chalcogen substitution from S to Se further modulates adsorption by enhancing surface polarizability. Structure plays a decisive role: metallic 1T phases promote stronger single-molecule adsorption due to enhanced electronic screening, whereas the more open coordination of the 2H phase provides greater configurational freedom at high hydrogen coverage. Janus functionalization introduces chemically inequivalent S- and Se-terminated surfaces, leading to side-dependent adsorption energies, hydrogen-layer thicknesses, and spatial distributions. Hydrogen uptake remains dominated by molecular physisorption across all systems. Finite-temperature AIMD simulations at 300 K demonstrate that hydrogen remains molecular even at high loadings, with no dissociation or irreversible chemisorption. 2H-NiSSe and 2H-PdSSe exhibit the most favorable combination of moderate adsorption energies, stable multilayer hydrogen configurations, and robust thermal stability, whereas Pt-based Janus systems display strong confinement and reduced reversibility. These results establish clear design principles for hydrogen storage in TMDs, showing that optimal performance arises from intermediate physisorption rather than maximal binding strength and highlighting Janus Ni- and Pd-based systems as promising platforms for reversible molecular hydrogen storage.

cond-mat.mtrl-sci↗

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↗

arXiv2023

Interaction of oxygen with pristine and defective MoS2 monolayers

Atom controlled sub-nanometer MoS$_2$ pores have been recently fabricated. Oxidative environments are of particular interest for MoS$_2$ applications in electronics, sensing and energy storage. In this work we carried out first-principles calculations of oxygen adsorption in plain and sub-nanometer MoS$_2$ nanopores. The chemical stability of the layers and pores towards oxygen was verified using density-functional theory. Dissociation and diffusion barriers have been calculated in order to understand surface and pore oxidation and its electronic properties at the atomic scale, which opens the path for future investigations of MoS$_2$ pores in a realistic environment.

cond-mat.mtrl-sci↗

arXiv2020

Pentaoctite phase: A new group V allotrope

By performing firt-principles electronic calculations we propose new a phase of group-V allotropes of antimonene, arsenene and phosphorene in the pentaoctite structure. By calculating the phonon spectra, we show that all these phases are stable. Whereas these structures have a indirect band gap, they can be made direct gap materials by applying external strain. GW calculations of the dielectric function demonstrate that all these structures have an absorption spectrum in the visible region, which could be useful for group-V optoelectronics.

cond-mat.mtrl-sci↗

arXiv2020

Chemical functionalization, electronic and dielectric properties of hybrid organic-tin layers

Band gap tuning and dielectric properties of small organic ligands adsorbed on tin monolayers (stanene) have been investigated using first-principles calculations. Charge density analysis using density-functional theory shows that the ligands are chemisorbed on stanene and some of the groups can open a band gap in the originally metallic statene. Furthermore many-body GW calculations demonstrate that the dielectric properties of bare and ligand adsorbed stanene have a large anisotropy. Our findings of a finite gap opens a path for rational theoretical design of functionalized two-dimensional stanene.

cond-mat.mtrl-sci↗

arXiv2020

Exploring charge density distribution and electronic properties of hybrid organic-germanium layers

Band gap tuning and dielectric properties of small organic ligands adsorbed on bidimensional germanium monolayers (germanene) have been investigated using first-principles calculations. We show that the adsorption of these small groups retains the initially stable free-standing pristine buckled germanium nanostructures. Charge density and chemical bonding analysis show that the ligands are chemisorbed on the germanium layers. Finally we demosntrate that the dielectric properties of bare and ligand adsorbed germanene have a large anisotropy. Our findings of a finite gap shows open a path for rational design of nanostructures with possible applications in biosensors and solar cells.

cond-mat.mtrl-sci↗

arXiv2019

Electronic, optical and charge transfer properties of topologically protected states in hybrid bismuthene layers

We have performed first-principles calculations of electronic and dielectric properties of single-layer bismuth (bismuthene) adsorbed with -COOH. We show that the Bi-COOH hybrid structure is a two-dimensional topological insulator with protected edge Dirac states. The adsorption process of -COOH induces a planar configuration to the initially pristine buckled bismuthene. We claim that the stability of these planar structure mainly stem from strain induced by the adsorption of the -COOH organic group, but it is also related to ligand-ligand interactions. Using charge density analysis we show that the role of this organic group is not only to stabilize the layer but also to functionalize it, which is very important for future applications such as sensing, biomolecules immobilization, as well in electronic spintronic and even optical devices, due to its large band gap. Finally we demonstrate that many body corrections are crucial to obtain a better description of the electronic and dielectric properties of these systems.

cond-mat.mtrl-sci↗

arXiv2018

Electronic and Optical Properties of Functionalized GaN (10-10) Surfaces using Hybrid-Density Functionals

Adsorption of small ligands on semiconductor surfaces is a possible route to modify these surfaces so that they can be used in biosensing and optoelectronic devices. In this work we perform density-functional theory calculations of electronic and optical properties of small ligands on GaN-(10$\bar1$0) surfaces. From the investigated anchor groups we show that thiol groups introduce states into the GaN band gap. However, these state are not optically active, at least for these perfect surfaces. This means that more realistic surfaces need to be considered to suggest how surface modification can enhance the optical properties of GaN non-polar surfaces.

cond-mat.mtrl-sci↗