arXiv subjects

J. M. De Sousa

Publications and source records attributed to J. M. De Sousa.

13 recordsLinked to original sources

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

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

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

Atomistic Computational Modeling of Temperature Effects in Fracture Toughness and Degradation of Penta-graphene Monolayer

The novel carbon allotrope with particular and unique 2D arrangement of carbon atoms similar to a Cairo pentagonal tiling, with interplay of $sp^{3}$ and $sp^{2}$ hybridized carbon atoms is called of Penta-graphene (PG). Previous theoretical investigations have shown that PG monolayer is mechanically and thermodynamically stable, possessing also a large band gap of $3.25eV$. This new carbon allotrope with unique carbon atom arrangement in a network (non-coplanar pentagons) is the focus of the theoretical investigations in this work. Using the non-equilibrium molecular dynamics simulations with reactive modern force field ReaxFF, we performed computational modeling of the nanostructural, dynamics e mechanical properties of penta-graphene monolayer under high temperature conditions. We obtained in our results the effect of the temperature in mechanical properties of penta-graphene monolayer up to $2000K$, where our results show that strain rate was strong effect on the mechanical properties with reduction of the $67$\%, reduction in the Ultimate Tensile Streght (UTS) $ 35.88 - 11.83GPa.nm $ and Young's Modulus ($Y_{Mod}$) of the $ 227.15 - 154.76GPa.nm $. In this work we also calculated the reactive degradation of monolayer of penta-graphene at temperatures changes of $10K$ up to $2000K$. Thus, our averages show that penta-graphene monolayer loss atomic configurations with temperature effect up to $600K$, where the monolayer show nanostructural transition with several islands of graphene, large regions of porosity, small 1D carbon chains, and also negative curved layer.

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↗

arXiv2020

Carbon Nanotube Peapods Under High-Strain Rate Conditions: A Molecular Dynamics Investigation

New forms of carbon-based materials have received great attention, and the developed materials have found many applications in nanotechnology. Interesting novel carbon structures include the carbon peapods, which are comprised of fullerenes encapsulated within carbon nanotubes. Peapod-like nanostructures have been successfully synthesized, and have been used in optical modulation devices, transistors, solar cells, and in other devices. However, the mechanical properties of these structures are not completely elucidated. In this work, we investigated, using fully atomistic molecular dynamics simulations, the deformation of carbon peapods under high-strain rate conditions, which are achieved by shooting the peapods at ultrasonic velocities against a rigid substrate. Our results show that carbon peapods experience large deformation at impact, and undergo multiple fracture pathways, depending primarily on the relative orientation between the peapod and the substrate, and the impact velocity. Observed outcomes include fullerene ejection, carbon nanotube fracture, fullerene, and nanotube coalescence, as well as the formation of amorphous carbon structures.

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↗

arXiv2019

Mathematical methods of diagonalization of quadratic forms applied to the study of stability of thermodynamic systems

In this paper, we use quadratic forms diagonalization methods applied to the function thermodynamic energy to analyze the stability of physical systems. Taylor's expansion was useful to write a quadratic expression for the energy function. We consider the same methodology to expanding the thermodynamic entropy and investigate the signs of the second-order derivatives of the entropy as well as previously to the thermodynamic energy function. The signs of the second-order derivatives to the Helmholtz, enthalpy and Gibbs functions are also analysed. We show the immediate consequences on the stability of physical systems due to the signs or curvatures of the second-order derivatives of these thermodynamic functions. The thermodynamic potentials are presented and constructed pedagogically as well as demonstrated the main mathematical aspects these surfaces. We demonstrate the power of superposition of mathematical and physical aspects to understand the stability of thermodynamic systems. Besides, we provide a consistent mathematical demonstration of the minimum, maximum, and saddle conditions of the potentials. We present here a detailed approach on aspects related to the curvature of the thermodynamic functions of physical interest with consequences on stability. This work can be useful as a part or supplement material of the traditional physics curriculum that requires a solid formation in thermodynamics, particularly about formal aspects on the stability.

cond-mat.stat-mech↗

arXiv2019

Elastic Properties of Graphyne-based Nanotubes

Graphyne nanotubes (GNTs) are nanostructures obtained from rolled up graphyne sheets, in the same way carbon nanotubes (CNTs) are obtained from graphene ones. Graphynes are 2D carbon-allotropes composed of atoms in sp and sp2 hybridized states. Similarly to conventional CNTs, GNTs can present different chiralities and electronic properties. Because of the acetylenic groups (triple bonds), GNTs exhibit large sidewall pores that influence their mechanical properties. In this work, we studied the mechanical response of GNTs under tensile stress using fully atomistic molecular dynamics simulations and density functional theory (DFT) calculations. Our results show that GNTs mechanical failure (fracture) occurs at larger strain values in comparison to corresponding CNTs, but paradoxically with smaller ultimate strength and Young's modulus values. This is a consequence of the combined effects of the existence of triple bonds and increased porosity/flexibility due to the presence of acetylenic groups.

cond-mat.mtrl-sci↗