arXiv subjects

Douglas S. Galvão

Publications and source records attributed to Douglas S. Galvão.

At least 37 records · Page 2Linked to original sources

arXiv2025

$β$-Irida-Graphene: A New 2D Carbon Allotrope for Sodium-Ion Battery Anodes

The quest for sustainable and efficient energy storage has driven the exploration of sodium-ion batteries (SIBs) as promising alternatives to lithium-ion systems. However, the larger ionic radius of sodium poses intrinsic challenges such as slow diffusion and structural strain in conventional electrode materials. As a contribution to addressing these limitations, the \b{eta}-Irida-graphene ($β$-IG) is herein introduced, a novel two-dimensional (2D) carbon allotrope derived from Irida-graphene, featuring a diverse polygonal lattice of 3-, 4-, 6-, 8-, and 9-membered carbon rings. Through density functional theory and ab initio molecular dynamics simulations, $β$-IG demonstrated remarkable thermal, dynamical, and mechanical stability, coupled with intrinsic conductive character and efficient sodium-ion mobility (energy barriers < 0.30 eV). Furthermore, the adsorption of sodium ions was energetically favorable, delivering an impressive predicted specific capacity of 554.5 mAh/g. The reported findings highlight $β$-IG as a good potential anode candidate for next-generation SIBs, offering high-rate performance and structural robustness, and expanding the functional design space for advanced carbon-based electrode materials.

cond-mat.mtrl-sci↗

arXiv2025

TPHE-Graphene: A First-Principles Study of a New 2D Carbon Allotrope for Hydrogen Storage

The shift from fossil fuels to renewable energy sources is essential for reducing global carbon emissions and addressing climate change. Developing advanced materials for efficient hydrogen storage enables sustainable energy solutions in this context. Herein, we propose sodium-decorated TPHE-graphene as a high-performance two-dimensional material for hydrogen storage. Density functional theory (DFT) calculations demonstrate that TPHE-graphene exhibits dynamical, thermal, energetic, and mechanical stability, as confirmed by cohesive energy, phonon dispersion, and molecular dynamics simulations. The monolayer displays metallic behavior and a high Young's modulus of 250.46 N/m. Upon sodium decoration, strong chemisorption occurs with a binding energy of -2.08 eV and minimal tendency for Na atom clustering. Hydrogen adsorption analysis reveals that each Na atom can bind up to five H$_2$ molecules, resulting in a gravimetric storage capacity of 9.52 wt\%. The calculated H$_2$ adsorption energies range from -0.22 eV to -0.18 eV, falling within the ideal range for reversible adsorption under ambient conditions. These findings highlight Na-decorated TPHE-graphene as a structurally robust and efficient hydrogen storage material well-suited for future green energy applications.

cond-mat.mtrl-sci↗

arXiv2025

Structural Stability of Sulfur Depleted MoS2

Transition metal dichalcogenides (TMDs), particularly monolayer MoS2, have received increased attention in materials science and have been exploited in diverse applications from photonics to catalysis. Defects in TMDs play a crucial role in modulating their properties, and understanding defect-induced dynamics is of great importance. This study investigates the dynamics of sulfur depletion in defective monolayer MoS2, which yields stable MoS monolayers. Various defect sizes, temperature regimes, and substrate effects were investigated. Through comprehensive classical molecular (ReaxFF) molecular dynamics (MD) and ab initio MD (AIMD) simulations, we elucidate the dynamics of sulfur vacancy formation in MoS2 lattices. After removing all sulfur atoms from the top layer, several sulfur atoms from the bottom layer spontaneously migrate to the top layer as a response to increase structural stability, thus creating a MoSx alloy. These findings deepen our understanding of defect dynamics in TMDs, offering valuable insights into the controlled engineering of their properties for nanotechnology applications.

cond-mat.mtrl-sci↗

arXiv2025

Unraveling Mn intercalation and diffusion in NbSe$_2$ bilayers through DFTB simulations

Understanding transition metal atoms' intercalation and diffusion behavior in two-dimensional (2D) materials is essential for advancing their potential in spintronics and other emerging technologies. In this study, we used density functional tight binding (DFTB) simulations to investigate the atomic-scale mechanisms of manganese (Mn) intercalation into NbSe$_2$ bilayers. Our results show that Mn prefers intercalated and embedded positions rather than surface adsorption, as cohesive energy calculations indicate enhanced stability in these configurations. Nudged elastic band (NEB) calculations revealed an energy barrier of 0.68 eV for the migration of Mn into the interlayer, comparable to other substrates, suggesting accessible diffusion pathways. Molecular dynamics (MD) simulations further demonstrated an intercalation concentration-dependent behavior. Mn atoms initially adsorb on the surface and gradually diffuse inward, resulting in an effective intercalation at higher Mn densities before clustering effects emerge. These results provide helpful insights into the diffusion pathways and stability of Mn atoms within NbSe$_2$ bilayers, consistent with experimental observations and offering a deeper understanding of heteroatom intercalation mechanisms in transition metal dichalcogenides.

cond-mat.mtrl-sci↗

arXiv2025

Athos-Graphene: Computational Discovery of an Art-Inspired 2D Carbon Anode for Lithium-Ion Batteries

Two-dimensional (2D) carbon allotropes have attracted growing interest for their structural versatility and potential in energy storage and nanoelectronics. We propose Athos-Graphene (AG), a novel 2D carbon allotrope inspired by the geometric patterns of Brazilian artist Athos Bulcão. Designed using density functional theory, AG features a periodic structure with high thermodynamic and thermal stability, as evidenced by a low cohesive energy of -7.96 eV/atom, the absence of imaginary phonon modes, and robust performance in ab initio molecular dynamics simulations up to 1000 K. It exhibits anisotropic mechanical properties, with Young's modulus values of 585 GPa and 600 GPa along the x- and y-directions, and Poisson's ratios of 0.19 and 0.17, respectively. Electronic structure analyses confirm its metallic behavior, while optical studies reveal anisotropic absorption in the visible and UV regions. For lithium-ion storage, Athos-Graphene shows strong Li adsorption (-2.3 to -1.0 eV), a high theoretical capacity of 836.78 mAh/g, and a low average open-circuit voltage of 0.54 V. Lithium diffusion barriers are as low as 0.3 eV on the surface and 0.66 eV between layers, with a high diffusion coefficient greater than 6x10^-6 cm^2/s. These features highlight AG as a promising anode material for high-performance lithium-ion batteries.

cond-mat.mtrl-sci↗

arXiv2025

Petal-Graphyne: A Novel 2D Carbon Allotrope for High-Performance Li and Na Ion Storage

Using density functional theory simulations, this study introduces Petal-Graphyne (PLG), a novel multi-ring metallic structure composed of 4-, 8-, 10-, and 16-membered rings. Its structural, electronic, and lithium/sodium storage properties were comprehensively investigated. PLG exhibits a high theoretical capacity of 1004 mAh/g for Li, Na, and mixed Li/Na ions, surpassing conventional graphite anodes. The material remains metallic, with multiple band crossings at the Fermi level. The optimal energy barriers for Li (0.28 eV) and Na (0.25 eV) on PLG and favorable diffusion coefficients in both monolayer and multilayer configurations are unveiled. The open circuit voltages are 0.47 V for Li, 0.51 V for Na, and 0.54 V for mixed-ion storage, suggesting stable electrochemical performance. These results highlight PLG as a promising candidate for next-generation lithium and sodium-ion batteries, combining high storage capacity and efficient ion transport.

cond-mat.mtrl-sci↗

arXiv2025

Physicochemical Characterization of a New 2D Semiconductor Carbon Allotrope, C16: An Investigation via Density Functional Theory and Machine Learning-based Molecular Dynamics

This study comprehensively characterizes, with suggested applications, a novel two-dimensional carbon allotrope, C$_{16}$, using Density Functional Theory and machine learning-based molecular dynamics. This nanomaterial is derived from naphthalene and bicyclopropylidene molecules, forming a planar configuration with sp$^2$ hybridization and featuring 3-, 4-, 6-, 8-, and 10-membered rings. Cohesive energy of \SI{-7.1}{\electronvolt/atom}, absence of imaginary frequencies in the phonon spectrum, and the retention of the system's topology after ab initio molecular dynamics simulations confirm the structural stability of C$_{16}$. The nanomaterial exhibits a semiconducting behavior with a direct band gap of \SI{0.59}{\electronvolt} and anisotropic optical absorption in the $y$ direction. Assuming a complete absorption of incident light, it registers a power conversion efficiency of \SI{13}{\percent}, demonstrating relatively good potential for applications in solar energy conversion. The thermoelectric figure of merit ($zT$) reaches 0.8 at elevated temperatures, indicating a reasonable ability to convert a temperature gradient into electrical power. Additionally, C$_{16}$ demonstrates high mechanical strength, with Young's modulus values of \SI{500}{\giga\pascal} and \SI{630}{\giga\pascal} in the $x$ and $y$ directions, respectively. Insights into the electronic, optical, thermoelectric, and mechanical properties of C$_{16}$ reveal its promising capability for energy conversion applications.

cond-mat.mtrl-sci↗

arXiv2025

Exploring Novel 2D Analogues of Goldene: Electronic, Mechanical, and Optical Properties of Silverene and Copperene

Two-dimensional (2D) materials have garnered significant attention due to their unique properties and broad application potential. Building on the success of goldene, a monolayer lattice of gold atoms, we explore its proposed silver and copper analogs, silverene and copperene, using density functional theory calculations. Our findings reveal that silverene and copperene are energetically stable, with formation energies of -2.3 eV/atom and -3.1 eV/atom, closely matching goldene's -2.9 eV/atom. Phonon dispersion and ab initio molecular dynamics simulations confirm their structural and dynamical stability at room temperature, showing no bond breaking or structural reconfiguration. Mechanical analyses indicate isotropy, with Young's moduli of 73 N/m, 44 N/m, and 59 N/m for goldene, silverene, and copperene, respectively, alongside Poisson's ratios of 0.46, 0.42, and 0.41. These results suggest comparable rigidity and deformation characteristics. Electronic band structure analysis highlights their metallic nature, with variations in the band profiles at negative energy levels. Despite their metallic character, these materials exhibit optical properties akin to semiconductors, pointing to potential applications in optoelectronics.

cond-mat.mtrl-sci↗

arXiv2024

Enhanced Elastocaloric Effects in γ-graphyne

The global emphasis on sustainable technologies has become a paramount concern for nations worldwide. Specifically, numerous sustainable methods are being explored as promising alternatives to the well-established vapor-compression technologies in cooling and heating devices. One such avenue gaining traction within the scientific community is the elastocaloric effect (eC). This phenomenon holds promise for efficient cooling and heating processes without causing environmental harm. Studies carried out at the nanoscale have demonstrated the efficiency of the eC, proving to be comparable to that of state-of-the-art macroscopic systems. In this study, we used classical molecular dynamics simulations to investigate the elastocaloric effect for γ-graphyne. Our analysis goes beyond obtaining changes in eC temperature and the coefficient of performance (COP) for two species of γ-graphyne nanoribbons (armchair and zigzag). We also explore their dependence on various conditions, including whether they are on deposited on a substrate or pre-strained. Our findings reveal a substantial enhancement in the elastocaloric effect for γ-graphyne nanoribbons when subjected to pre-strain, amplifying it by at least one order of magnitude. Under certain conditions, the change in the eC temperature and the COP of the structures reach expressive values as high as 224 K and 14, respectively. We discuss the implications of these results by examining the shape and behavior of the carbon-carbon bond lengths within the structures.

cond-mat.mes-hall↗

arXiv2024

Raman Spectra and Excitonic Effects of the novel Ta$_2$Ni$_3$Te$_5$ Monolayer

We have investigated the Raman spectrum and excitonic effects of the novel two-dimensional Ta$_2$Ni$_3$Te$_5$ structure. The monolayer is an indirect band gap semiconductor with an electronic band gap value of 0.09 eV and 0.38 eV, determined using GGA-PBE and HSE06 exchange-correlation functionals, respectively. Since this structure is energetically, dynamically, and mechanically stable, it could be synthesized as a free-standing material. We identify ten Raman and ten infrared active modes for various laser energies, including those commonly used in Raman spectroscopy experiments. It was also observed that the contribution of Ni atoms is minimal in most Raman vibrational modes. In contrast, most infrared vibrational modes do not involve the vibration of the Ta atoms. As far as the optical properties are concerned, this monolayer shows a robust linear anisotropy, an exciton binding energy of 287 meV, and also presents a high reflectivity in the ultraviolet region, which is more intense for linear light polarization along the x-direction.

cond-mat.mtrl-sci↗

arXiv2024

Irida-Graphene Phonon Thermal Transport via Non-equilibrium Molecular Dynamics Simulations

Recently, a new 2D carbon allotrope called Irida-Graphene (Irida-G) was proposed. Irida-G consists of a flat sheet topologically arranged into 3-6-8 carbon rings exhibiting metallic and non-magnetic properties. In this study, we investigated the thermal transport properties of Irida-G using classical reactive molecular dynamics simulations. The findings indicate that Irida-G has an intrinsic thermal conductivity of approximately 215 W/mK at room temperature, significantly lower than that of pristine graphene. This decrease is due to characteristic phonon scattering within Irida-G's porous structure. Additionally, the phonon group velocities and vibrational density of states for Irida-G were analyzed, revealing reduced average phonon group velocities compared to graphene. The thermal conductivity of Irida-G is isotropic and shows significant size effects, transitioning from ballistic to diffusive heat transport regimes as the system length increases. These results suggest that while Irida-G has lower thermal conductivity than graphene, it still holds potential for specific thermal management applications, sharing characteristics with other two-dimensional materials.

cond-mat.mtrl-sci↗

arXiv2024

Structural and Electronic Properties of Amorphous Silicon and Germanium Monolayers and Nanotubes: A DFT Investigation

A recent breakthrough has been achieved by synthesizing monolayer amorphous carbon (MAC), which introduces a material with unique optoelectronic properties. Here, we used ab initio (DFT) molecular dynamics simulations to study silicon and germanium MAC analogs. Typical unit cells contain more than 600 atoms. We also considered their corresponding nanotube structures. The cohesion energy values for MASi and MAGe range from -8.41 to -7.49 eV/atom and follow the energy ordering of silicene and germanene. Their electronic behavior varies from metallic to small band gap semiconductors. Since silicene, germanene, and MAC have already been experimentally realized, the corresponding MAC-like versions we propose are within our present synthetic capabilities.

cond-mat.mtrl-sci↗

arXiv2024

On the mechanical, thermoelectric, and excitonic properties of Tetragraphene monolayer

Two-dimensional carbon allotropes have attracted much attention due to their extraordinary optoelectronic and mechanical properties, which can be exploited for energy conversion and storage applications. In this work, we use density functional theory simulations and semi-empirical methods to investigate the mechanical, thermoelectric, and excitonic properties of Tetrahexcarbon (also known as Tetragraphene). This quasi-2D carbon allotrope exhibits a combination of squared and hexagonal rings in a buckled shape. Our findings reveal that tetragraphene is a semiconductor material with a direct electronic bandgap of 2.66 eV. Despite the direct nature of the electronic band structure, this material has an indirect exciton ground state of 2.30 eV, which results in an exciton binding energy of 0.36 eV. At ambient temperature, we obtain that the lattice thermal conductivity for tetragraphene is approximately 118 W/mK. Young's modulus and the shear modulus of tetragraphene are almost isotropic, with maximum values of 286.0 N/m and 133.7 N/m, respectively, while exhibiting a very low anisotropic Poisson ratio value of 0.09.

cond-mat.mtrl-sci↗

arXiv2023

Reversible Actuation of $α$-Borophene Nanoscrolls

In this work, we proposed and investigated the structural and electronic properties of boron-based nanoscrolls (armchair and zigzag) using the DFTB+ method. We also investigated the electroactuation process (injecting and removing charges). A giant electroactuation was observed, but the results show relevant differences between the borophene and carbon nanoscrolls. The molecular dynamics simulations showed that the scrolls are thermally and structurally stable for a large range of temperatures (up to 600K) and the electroactuation process can be easily tuned and can be entirely reversible for some configurations.

cond-mat.mes-hall↗

arXiv2023

Scalable synthesis and characterization of multilayer $γ$-graphyne, new carbon crystals with a small direct bandgap

$γ$-Graphyne is the most symmetric sp2/sp1 allotrope of carbon, which can be viewed as graphene uniformly expanded through insertion of two-carbon acetylenic units between all the aromatic rings. To date, synthesis of bulk $γ$-graphyne has remained a challenge. We here report the synthesis of multilayer $γ$-graphyne through crystallization-assisted irreversible cross-coupling polymerization. Comprehensive characterization of this new carbon phase is described, including synchrotron X-ray diffraction, electron diffraction, lateral force microscopy, Raman and infrared spectroscopy, and cyclic voltammetry. Experiments indicate that $γ$-graphyne is a 0.48 eV bandgap semiconductor, with a hexagonal a-axis spacing of 6.88 Å and an interlayer spacing of 3.48 Å, which is consistent with theoretical predictions. The observed crystal structure has an aperiodic sheet stacking. The material is thermally stable up to 240 $^\circ$C but undergoes a transformation at higher temperatures. While conventional 2D polymerizations and reticular chemistry rely on error correction through reversibility, we demonstrate that a periodic covalent lattice can be synthesized under purely kinetic control. The reported methodology is scalable and inspires extension to other allotropes of the graphyne family.

cond-mat.mtrl-sci↗

arXiv2022

A DFT Study of the Electronic, Optical, and Mechanical Properties of a Recently Synthesized Monolayer Fullerene Network

Closely packed quasi-hexagonal and quasi-tetragonal crystalline phase of C$_{60}$ molecules (named qHPC$_{60}$) was recently synthesized. Here, we used DFT simulations to investigate the electronic, optical, and mechanical properties of qHPC$_{60}$ monolayers. qHPC$_{60}$ has a moderate direct electronic bandgap, with anisotropic mechanical properties. Their elastic modulus ranges between 50 and 62 GPa. The results for optical properties suggest that qHPC$_{60}$ can act as UV collectors for photon energies until 5.5 eV since they present low reflectivity and refractive index greater than one. The estimated optical bandgap (1.5-1.6 eV) is in very good agreement with the experimental one (1.6 eV).

cond-mat.mtrl-sci↗

arXiv2021

Auxetic properties of a newly proposed $γ$-graphyne-like material

In this work, we propose a new auxetic (negative Poisson's ratio values) structure, based on a $γ$-graphyne structure, here named $AγG$ $structure$. Graphynes are 2D carbon allotropes with phenylic rings connected by acetylenic groups. The A$γ$G structural/mechanical and electronic properties, as well as its thermal stability, were investigated using classical reactive and quantum molecular dynamics simulations. We found that A$γ$G has a large bandgap of 2.48 eV and is thermally stable at a large range of temperatures. It presents a Young's modulus that is an order of magnitude smaller than that of graphene or $γ$-graphyne. The classical and quantum results are consistent and validate that the A$γ$G is auxetic, both when isolated (vacuum) and when deposited on a copper substrate. We believe that this is the densest auxetic structure belonging to the graphyne-like families.

cond-mat.mtrl-sci↗

arXiv2021

Controlling Movement at Nanoscale: Curvature Driven Mechanotaxis

Locating and manipulating nano-sized objects to drive motion is a time and effort consuming task. Recent advances show that it is possible to generate motion without direct intervention, by embedding the source of motion in the system configuration. In this work, we demonstrate an alternative manner to controllably displace nano-objects without external manipulation, by employing spiral-shaped carbon nanotube (CNT) and graphene nanoribbon structures (GNR). The spiral shape contains smooth gradients of curvature, which lead to smooth gradients of bending energy. We show these gradients can drive nanoscillators. We also carry out an energy analysis by approximating the carbon nanotube to a thin rod and discuss how torsional gradients can be used to drive motion. For the nanoribbons, we also analyzed the role of layer orientation. Our results show that motion is not sustainable for commensurate orientations, in which AB stacking occurs. For incommensurate orientations, friction almost vanishes, and in this instance, the motion can continue even if the driving forces are not very high. This suggests that mild curvature gradients, which can already be found in existing nanostructures, could provide mechanical stimuli to direct motion.

cond-mat.mes-hall↗