arXiv subjects

D. S. Galvão

Publications and source records attributed to D. S. Galvão.

At least 19 recordsLinked to original sources

arXiv2025

Novel 3D Pentagraphene Allotropes: Stability, Electronic, Mechanical, and Optical Properties

Carbon-based materials have attracted great attention due to their exceptional structural diversity and wide-ranging applications. Recently, a new two-dimensional carbon allotrope, named pentagraphene (PG), was proposed. In this study, we proposed three novel three-dimensional (3D) PG allotropes, named 3D-PG-$α$, -$β$, and -$γ$, engineered through biaxial strain and controlled compression of 2D PG layers. Comprehensive stability analyses, including phonon dispersion and ab initio molecular dynamics simulations (AIMD), confirm their thermodynamic stability under room and high-temperature conditions. 3D-PG-$α$ is the most stable, exhibiting a cohesive energy 0.5 eV/atom lower than the least stable structure, 3D-PG-$γ$. Electronic property characterization reveals semiconducting behavior for all structures, with indirect electronic band gaps ranging from 0.91 to 2.67 eV. The analyses of the mechanical properties showed significant anisotropy, with higher stiffness along the in-plane ($xy$-plane) direction. Optical properties highlight strong absorption along a wide range and a pronounced anisotropic response. Additionally, the absorption spectra exhibit activity in the visible region, and the refractive index and reflectivity indicate potential use in ultraviolet-blocking devices.

cond-mat.mtrl-sci↗

arXiv2025

Entangled Interlocked Diamond-like (Diamondiynes) Lattices

Diamondynes, a new class of diamond-like carbon allotropes composed of carbon with sp$^2$/sp$^3$-hybridized carbon networks, exhibit unique structural motifs that have not been previously reported in carbon materials. These architectures feature sublattices that are both interlocked and capable of relative movement. Using ab initio simulations, we have conducted an extensive investigation into the structural and electronic properties of five diamondyne structures. Our results show that diamondiynes are thermodynamically stable and exhibit wide electronic band gaps, from 2.2 eV to 4.0 eV. They are flexible yet highly resistant compared to other diamond-like structures. They have relatively small cohesive energy values, consistent with the fact that one diamondyne structure (2f-unsym) has already been experimentally realized. Our results provide new physical insights into diamond-like carbon networks and suggest promising directions for the development of porous, tunable frameworks with potential applications in energy storage and conversion.

cond-mat.mtrl-sci↗

arXiv2024

Exploring the Electronic and Mechanical Properties of the Recently Synthesized Nitrogen-Doped Monolayer Amorphous Carbon

The recent synthesis of nitrogen-doped monolayer amorphous carbon (MAC @N) opens new possibilities for multifunctional materials. In this study, we have investigated the nitrogen doping limits and their effects on MAC@N's structural and electronic properties using density functional-based tight-binding simulations. Our results show that MAC@N remains stable up to 35\% nitrogen doping, beyond which the lattice becomes unstable. The formation energies of MAC@N are higher than those of nitrogen-doped graphene for all the cases we have investigated. Both undoped MAC and MAC@N exhibit metallic behavior, although only MAC features a Dirac-like cone. MAC has an estimated Young's modulus value of about 410 GPa, while MAC@N's modulus can vary around 416 GPa depending on nitrogen content. MAC displays optical activity in the ultraviolet range, whereas MAC@N features light absorption within the infrared and visible ranges, suggesting potential for distinct optoelectronic applications. Their structural thermal stabilities were addressed through molecular dynamics simulations. MAC melts at approximately 4900K, while MAC@N loses its structural integrity for temperatures ranging from 300K to 3300K, lower than graphene. These results point to potential MAC@N applications in flexible electronics and optoelectronics.

cond-mat.mtrl-sci↗

arXiv2023

Lattice Thermal Conductivity of 2D Nanomaterials: A Simple Semi-Empirical Approach

Extracting reliable information on certain physical properties of materials, like thermal behavior, such as thermal transport, which can be very computationally demanding. Aiming to overcome such difficulties in the particular case of lattice thermal conductivity (LTC) of 2D nanomaterials, we propose a simple, fast, and accurate semi-empirical approach for its calculation.The approach is based on parameterized thermochemical equations and Arrhenius-like fitting procedures, thus avoiding molecular dynamics or \textit{ab initio} protocols, which frequently demand computationally expensive simulations. As proof of concept, we obtain the LTC of some prototypical physical systems, such as graphene (and other 2D carbon allotropes), hexagonal boron nitride (hBN), silicene, germanene, binary, and ternary BNC latices and two examples of the fullerene network family. Our values are in good agreement with other theoretical and experimental estimations, nonetheless being derived in a rather straightforward way, at a fraction of the computational cost.

cond-mat.mtrl-sci↗

arXiv2023

Nanomechanical behavior of pentagraphyne-based single-layer and nanotubes through reactive classical molecular dynamics

In a recent theoretical study, a new 2D carbon allotrope called pentagraphyne (PG-yne) was proposed. This allotrope is derived from pentagraphene by introducing acetylenic linkages between sp3 and sp2 hybridized carbon atoms. Due to its interesting electronic and structural properties, it is of interest to investigate the mechanical behavior of PG-yne in both monolayer and nanotube topologies. To achieve this, we performed fully atomistic reactive (ReaxFF) molecular dynamics simulations, and our results show that Young's modulus average of PG-yne monolayers is approximately 913 GPa, at room temperature. In comparison, it ranges from 497-789 GPa for the nanotubes studied. Furthermore, we observed that PG-yne monolayers exhibit a direct transition from elastic to complete fracture under critical strain without a plastic regime. In contrast, some PG-yne nanotubes exhibit an extended flat plastic regime before total fracture.

physics.comp-ph↗

arXiv2023

First-Principles and Reactive Molecular Dynamics Study of the Elastic Properties of Pentahexoctite-based Nanotubes

Pentahexoctite (PH) is a pure sp$^2$ hybridized planar carbon allotrope whose structure consists of a symmetric combination of pentagons, hexagons, and octagons. The proposed PH structure was shown to be an intrinsically metallic material exhibiting good mechanical and thermal stability. PH nanotubes (PHNTs) have also been proposed, and their properties were obtained from first principles calculations. Here, we carried out fully-atomistic simulations, combining reactive (ReaxFF) molecular dynamics (MD) and density functional theory (DFT) methods, to study the PHNTs elastic properties and fracture patterns. We have investigated the mechanical properties behavior as a function of the tube diameter and temperature regimes. Our results showed that the PHNTs, when subjected to large tensile strains, undergo abrupt structural transitions exhibiting brittle fracture patterns without a plastic regime.

cond-mat.mtrl-sci↗

arXiv2022

2D Porphyrazine: A New Nanoporous Material

Crystalline microporous materials are solids formed by interconnected pores of less than 2 nm in size. Typically, they possess large surface areas desirable for versatile applications such as catalysis, gas adsorption, and energy storage. In the present work, we propose a new porphyrin-based 2D nanoporous crystal, named 2D Porphyrazine (2DP), which is formed by topological assembling H$_{5}$C$_{13}$N$_{4}$ porphyrins. We have considered its monolayer, bi-layer, and molecular crystal (bulk) arrangements. We carried out DFT calculations to investigate 2DP structural and electronic properties. Results show that 2DP is a very stable structure with a direct bandgap of 0.65 eV and significant optical absorption in the visible range. 2DP exhibited satisfactory affinity to lithium atoms. Simulations also showed the existence of proton transfer between nitrogen atoms. It is the first report on the site-specific hydrogen exchange process in 2D crystals.

cond-mat.mtrl-sci↗

arXiv2022

Boron Nitride Nanotube Peapod under Ultrasonic Velocity Impacts: A Fully Atomistic Molecular Dynamics Investigation

In this work, we investigated the mechanical response and fracture dynamics of boron nitride nanotubes (BNNTs)-peapods under ultrasonic velocity impacts (from 1 km/s to 6 km/s) against a solid target. BNNT-peapods are BNNTs containing an encapsulated linear arrangement of C60 molecules. We carried out fully atomistic reactive (ReaxFF) molecular dynamics simulations. We have considered the case of horizontal and vertical shootings. Depending on the velocity values we observed tube bending, tube fracture, and C60 ejection. One interesting result was tube unzipping with the formation of bilayer nanoribbons 'incrusted' with C60 molecules.

cond-mat.mtrl-sci↗

arXiv2022

Dynamical Formation of Graphene and Graphane Nanoscrolls

Carbon nanoscrolls (CNSs) are nanomaterials with geometry resembling graphene layers rolled up into a spiral (papyrus-like) form. Effects of hydrogenation and temperature on the self-scrolling process of two nanoribbons interacting with a carbon nanotube (CNT) have been studied by molecular dynamics simulations for three configurations: (1) graphene/graphene/CNT; (2) graphene/graphane/CNT, and (3) graphane/graphane/CNT. Graphane refers to a fully hydrogenated graphene nanoribbon. Nanoscroll formation is observed for configurations (1) and (2) for temperatures 300-1000 K, while nanoribbons wrap CNT without nanoscroll formation for configuration (3).

cond-mat.mtrl-sci↗

arXiv2022

Thermal Stability and Fracture Patterns of a Recently Synthesized Monolayer Fullerene Network: A Reactive Molecular Dynamics Study

New monolayer 2D carbon structures, namely qHPC60 and qTPC60, were recently synthesized by covalently bonding C60 polymers. Here, we carried out Reactive (ReaxFF) molecular dynamics simulations to study the thermodynamic stability and fracture patterns of qHPC60 and qTPC60. Our results showed that these structures present similar thermal stability, with sublimation points of 3898K and 3965K, respectively. qHPC60 and qTPC60 undergo an abrupt structural transition becoming totally fractured after a critical strain threshold. The crack propagation is linear (non-linear) for qHPC60 (qTPC60). The estimated elastic modulus for qHPC60 and qTPC60 are 175.9 GPa and 100.7 GPa, respectively.

cond-mat.mtrl-sci↗

arXiv2022

Fully Atomistic Molecular Dynamics Simulations of Elastic Properties of Tetragraphene Monolayer

A quasi-2D semiconductor carbon allotrope called tetrahexcarbon, also named tetragraphene, was recently proposed featuring an unusual structure combining squared and hexagonal rings. Mechanical and electronic properties of tetragraphene have been predicted based on first-principles Density Functional Theory (DFT) calculations. However, a comprehensive study of its mechanical behavior under different temperatures is still lacking. In this work, using fully atomistic reactive molecular dynamics (MD) simulations, we investigate the mechanical properties of monolayer tetragraphene under tensile strain from the linear regime up to the complete structural failure (fracture). Different temperatures were considered and the results were compared to that of two other known planar carbon allotropes: graphene and penta-graphene. One interesting result is that tetragraphene experiences a transition from crystalline to an amorphous structure by either temperature or tension application. At room temperature, the critical strains along the two orthogonal unit-cell directions of tetragraphene are 38\% and 30\%, which is higher than that for graphene and penta-graphene. Tetragraphene Young's modulus values along its directions are from three to six times smaller than that of graphene and about 57\% that of penta-graphene at room temperature. Ultimate tensile strength values along the two directions of tetragraphene were obtained and also shown to be smaller than that of graphene and penta-graphene.

cond-mat.mtrl-sci↗

arXiv2022

A Computational Study On the Mechanical Properties of Pentahexoctite Single-layer: Combining DFT and Classical Molecular Dynamics Simulations

Studies aimed at designing new allotropic forms of carbon have received much attention. Recently, a new 2D graphene-like allotrope named Pentahexoctite was theoretically proposed. Pentahexoctite has a metallic signature, and its structure consists of continuous 5-6-8 rings of carbon atoms with sp2 hybridization. Here, we carried out fully-atomistic computational simulations, combining reactive (ReaxFF) molecular dynamics (MD) and density functional theory (DFT) methods, to study the elastic properties and fracture patterns of Pentahexoctite monolayer. Results revealed a Young's Modulus of 0.74 TPa, smaller than the graphene one (about 1.0 TPa). The Pentahexoctite monolayer, when subjected to a critical strain, goes directly from elastic to completely fractured regimes. This process occurs with no plasticity stages between these two regimes. Importantly, graphene presents a similar fracture process. The elastic properties calculated with both DFT and MD are in good agreement. Keywords: Reactive Molecular Dynamics, DFT, Mechanical Properties, Carbon Allotrope,

cond-mat.mtrl-sci↗

arXiv2021

On the Thermomechanical Properties and Fracture Patterns of the Novel Nonbenzenoid Carbon Allotrope (Biphenylene Network): A Reactive Molecular Dynamics Study

Recently, a new two-dimensional carbon allotrope, named biphenylene network (BPN) was experimentally realized. The BPN structure is composed of four-, six-, and eight-membered rings of sp$^2$-hybridized carbon atoms. In this work, we carried out fully-atomistic reactive (ReaxFF) molecular dynamics simulations to study the thermomechanical properties and fracture patterns of non-defective and defective (nanocracks) BPN. Our results show that under uniaxial tensile loading, BPN is converted into four distinct morphologies before fracture starts. This conversion process is dependent on the stretching direction. Some of the formed structures are mainly formed by eight-membered rings, which have different shapes in each morphology. In one of them, a graphitization process was observed before the complete fracture. Importantly, in the presence of nanocracks, no new morphologies are formed. BPN exhibits a distinct fracture process when contrasted to graphene. After the critical strain threshold, the graphene transitions from an elastic to a brittle regime, while BPN can exhibit different inelastic stages. These stages are associated with the appearance of new morphologies. However, BPN shares some of the exceptional graphene properties. Its calculated Young's modulus and melting point values are comparable to the graphene ones, about 1019.4 GPa and 4024K, respectively.

cond-mat.mtrl-sci↗

arXiv2021

Dynamics and Structural Transformations of Carbon Onion-Like under High-Velocity Impacts

Carbon nano-onions (CNO) are multi-shell fullerenes. In the present work, we used fully atomistic reactive (ReaxFF) molecular dynamics simulations to study the dynamics and structural transformations of CNO structures under high-velocity impacts against a fixed and rigid substrate. We considered single and multi-shell CNO (up to six shells) and at different impact velocities (from 2 up to 7 Km/s). Our results indicated three regimes formed after the CNO impact: slightly deformed CNO (quasi-elastic collision, below 2.0 Km/s), collapsed CNO (inelastic collisions, between 3.0 and 5.0 Km/s) forming a diamondoid-like core, and fragmented CNO yielding linear atomic carbon chains (above 5.0 Km/s). We also discussed the dynamical reconfiguration of carbon-carbon bonds during the collision process. The impact of CNO against the substrate yielded $sp^3$-like bond types for all the used initial velocities. At intermediate velocities (between 3.0 and 5.0 Km/s), the inelastic collision forms diamondoid-like cores by converting a substantial quantity of $sp^2$ bonds into $sp^3$ ones. In the high velocities regime, the total number of $sp^1$, $sp^2$, and $sp^3$ bonds tend to be similar.

cond-mat.mtrl-sci↗

arXiv2020

On the Mechanical Properties of Popgraphene-based Nanotubes: a Reactive Molecular Dynamics Study

Carbon-based tubular materials have sparked a great interest for future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of $5-8-5$ rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ($(n,0)$ and $(0,n)$) and/or diameters and at different temperatures (from 300 up to 1200K). Results showed that the tubes are thermally stable (at least up to 1200K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ($(0,n)$) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ($(n,0)$). Moreover, it was obtained that the Young's modulus ($Y_{Mod}$) (750-900 GPa) and ultimate strength ($σ_{US}$) (120-150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. $Y_{Mod}$ values obtained for PopNTs are not significantly temperature dependent. While the $σ_{US}$ values for the $(0,n)$ showed a quasi-linear dependence with the temperature, the $(n,0)$ exhibited no clear trends.

cond-mat.mtrl-sci↗

arXiv2020

On the Elastic Properties of Single-Walled Phagraphene Nanotubes

Phagraphene (PhaG) is a quasi-planar 2D structure composed of $5-6-7$ ring sequence. We have investigated the structural and mechanical properties of phagraphene nanotubes (PhaNTs) through fully atomistic reactive molecular dynamics (MD) simulations. For comparison purposes, the results were also contrasted to similar carbon nanotubes (CNTs). Results showed that PhaNTs and CNTs present similar brittle fracture mechanisms. The Young's modulus values obtained for PhaNTs were smaller than the corresponding ones for CNTs. Both, PhaNTs and CNTs, present equivalent fracture strains ranging between 15\%-20\%. For the ultimate strength values, CNTs present values about 30\% higher than the corresponding ones for PhaNTs.

cond-mat.mtrl-sci↗

arXiv2019

Elastic and Fracture Properties of Single Walled Pentagraphene Nanotubes

Membranes of carbon allotropes comprised solely of densely packed pentagonal rings, known as pentagraphene, exhibit negative Poisson's ratio (auxetic behavior) and a bandgap of $3.2$ eV. In this work, we investigated the structural stability, mechanical and fracture properties of nanotubes formed by rolling up pentagraphene membranes, the so-called pentagraphene nanotubes (PGNTs). Single-walled PGNT of three distinct configurations: zigzag, $α$-armchair, and $β$-armchair were studied combining first-principles calculations and reactive molecular dynamics simulations. Our results showed Young's modulus values of $680-800 GPa$, critical strain of $18-21\%$, and ultimate tensile stress of $85-110 GPa$. We also observed auxetic behavior. During stretching at room temperature, we observed a transition between $β$-armchair to $α$-armchair PGNT close to the critical strain. With relation to fracture patterns, we observed that mechanical failure starts at bonds mostly aligned to the stretching direction and after tube radial collapse.

cond-mat.mtrl-sci↗

arXiv2018

Differences in the Mechanical Properties of Monolayer and Multilayer WSe2/MoSe2

Transition metal dichalcogenides are 2D structures with remarkable electronic, chemical, optical and mechanical properties. Monolayer and crystal properties of these structures have been extensively investigated, but a detailed understanding of the properties of their few-layer structures are still missing. In this work we investigated the mechanical differences between monolayer and multilayer WSe2 and MoSe2, through fully atomistic molecular dynamics simulations (MD). It was observed that single layer WSe2/MoSe2 deposited on silicon substrates have larger friction coefficients than 2, 3 and 4 layered structures. For all considered cases it is always easier to peel off and/or to fracture MoSe2 structures. These results suggest that the interactions between first layer and substrate are stronger than interlayer interactions themselves. Similar findings have been reported for other nanomaterials and it has been speculated whether this is a universal-like behavior for 2D layered materials. We have also analyzed fracture patterns. Our results show that fracture is chirality dependent with crack propagation preferentially perpendicular to W(Mo)-Se bonds and faster for zig-zag-like defects.

cond-mat.mes-hall↗