arXiv subjects

Md Mahbubul Islam

Publications and source records attributed to Md Mahbubul Islam.

13 recordsLinked to original sources

arXiv2023

High Pressure and Temperature Neural Network Reactive Force Field for Energetic Materials

Reactive force fields for molecular dynamics have enabled a wide range of studies in numerous material classes. These force fields are computationally inexpensive as compared to electronic structure calculations and allow for simulations of millions of atoms. However, the accuracy of traditional force fields is limited by their functional forms, preventing continual refinement and improvement. Therefore, we develop a neural network based reactive interatomic potential for the prediction of the mechanical, thermal, and chemical response of energetic materials at extreme conditions for energetic materials. The training set is expanded in an automatic iterative approach and consists of various CHNO materials and their reactions under ambient and under shock loading conditions. This new potential shows improved accuracy over the current state of the art force fields for a wide range of properties such as detonation performance, decomposition product formation, and vibrational spectra under ambient and shock loading conditions.

cond-mat.mtrl-sci↗

arXiv2022

Data-Driven Machine Learning to Predict Mechanical Properties of Monolayer TMDs

The understanding of the material properties of the layered transition metal dichalcogenides (TMDs) is critical for their applications in structural composites. The data-driven machine learning (ML) based approaches are being developed in contrast to traditional experimental or computational approach to predict and understand materials properties under varied operating conditions. In this study, we used two ML algorithms such as Long Short-Term Memory (LSTM) and Feed Forward Neural Network (FFNN) combined with molecular dynamics (MD) simulations to predict the mechanical properties of MX2 (M = Mo, W, and X = S, Se) TMDs. The LSTM model is found to be capable of predicting the entire stress-strain response whereas the FFNN is used to predict the material properties such as fracture stress, fracture strain, and Young's modulus. The effects of operating temperature, chiral orientation, and pre-existing crack size on the mechanical properties are thoroughly investigated. We carried out 1440 MD simulations to produce the input dataset for the neural network models. Our results indicate that both LSTM and FFNN are capable of predicting the mechanical response of monolayer TMDs under different conditions with more than 95% accuracy. The FFNN model exhibits lower computational cost than LSTM; however, the capability of LSTM model to predict the entire stress-strain curve is advantageous to assess material properties. The study paves the pathway toward extending this approach to predict other important properties, such as optical, electrical, and magnetic properties of TMDs.

cond-mat.mtrl-sci↗

arXiv2021

MEAM parameterization for cyclic and tensile deformations of Gold-Silver core-shell systems

Gold-Silver (Au-Ag) core-shell nanostructures are gaining importance in stretchable electronics where high tensile and fatigue resistance is of paramount importance. This work proposes the parameterization of a modified embedded atomic model (MEAM) interatomic potential through density functional theory (DFT) calculations for investigating the role of dislocations and defect interaction governing the mechanical behavior of Au-Ag and Ag-Au Core-shell nanostructures under tensile and fatigue loading using molecular dynamics (MD) simulations. A comparative analysis between the Core-shell structures and their pristine counterparts is also conducted. Throughout this work, pseudo-potential and all-electron full potential DFT schemes are used for parameterizing MEAM by calculating cohesive energy, lattice parameter, and bulk modulus of pure Au, Ag and their alloy. Using the new force-field for MD simulations, the tensile behavior of pristine and core-shell nanowires is explored for temperatures between 300K to 600K. The fatigue properties of two pristine and two core-shell nanowires in a strain range of -15% to 15% for 10 cycles is also conducted. Our results suggest that Ag-Au Core-shell nanowire shows the best reversibility under fatigue loading among the structures examined. Moreover, Ag-Au exhibit the highest dislocation formation and complete annihilation of defects consistently. While, Au-Ag present improved fatigue properties than its pristine counterparts but have some residual defects leading to lower reversibility when compared to Ag-Au. For tensile loading, all four structures exhibited deterioration in strength with increasing temperature. Thermal softening is seen to be more prominent in Au-Ag core-shell nanowires compared to Ag-Au.

cond-mat.mtrl-sci↗

arXiv2020

Nanomechanics of Antimonene Allotropes

Monolayer antimonene has drawn the attention of research communities due to its promising physical properties. But mechanical properties of antimonene is still largely unexplored. In this work, we investigate the mechanical properties and fracture mechanisms of two stable phases of monolayer antimonene -- the $α$ antimonene ($α$-Sb) and the $β$ antimonene ($β$-Sb), through molecular dynamics (MD) simulations. Our simulations reveal that stronger chiral effect results in a greater anisotropic elastic behavior in $β$-antimonene than in $α$-antimonene. In this paper we focus on crack-tip stress distribution using local volume averaged virial stress definition and derive the fracture toughness from the crack-line stress. Our calculated crack tip stress distribution ensures the applicability of linear elastic fracture mechanics (LEFM) for cracked antimonene allotropes with considerable accuracy up to a pristine structure. We evaluate the effect of temperature, strain rate, crack-length and point-defect concentration on the strength and elastic properties. Tensile strength goes through significant degradation with the increment of temperature, crack length and defect percentage. Elastic modulus is less susceptible to temperature variation but is largely affected by the defect concentration. Strain rate induces a power law relation between strength and fracture strain. Finally, we discuss the fracture mechanisms in the light of crack propagation and establish the links between the fracture mechanism and the observed anisotropic properties.

cond-mat.mtrl-sci↗

arXiv2020

Mechanical and Vibrational Characteristics of Functionally Graded Cu-Ni Nanowire: A Molecular Dynamics Study

Functionally graded material (FGM) is a class of advanced materials, consisting of two (or more) different constituents, that possesses a continuously varying composition profile. With the advancement of nanotechnology, applications of FGMs have shifted from their conventional usage towards sophisticated micro and nanoscale electronics and energy conversion devices. Therefore, the study of mechanical and vibrational properties of different FGM nanostructures is crucial in exploring their feasibility for different applications. In this study, for the first time, we employed molecular dynamics (MD) simulations to investigate the mechanical and vibrational properties of radially graded Cu-Ni FGM nanowires (NW). Distribution of Cu and Ni along the radial direction follows power-law, exponential and sigmoid functions for FGM NWs under consideration. Our results demonstrate that, distribution function parameters play an important role in modulating the mechanical (elastic modulus and ultimate tensile strength) and vibrational (natural frequency and quality factor) properties of FGM NWs. The study also suggests that, elastic moduli of FGM NWs can be predicted with relatively good accuracy using Tamura and Reuss micromechanical models, regardless of NW diameter. We found that, Euler-Bernoulli beam theory under-predicts the natural frequencies of FGM NWs, whereas He-Lilley model closely approximates the MD results. Interestingly, FGM NWs are always found to exhibit beat vibration because of their asymmetrical cross sections. Finally, this is the first atomistic scale study of FGMs that directly compares MD simulations with continuum theories and micromechanical models to understand the underlying mechanisms that govern the mechanical and vibrational properties of FGM NWs in nanoscale.

cond-mat.mtrl-sci↗

arXiv2020

Mechanical Properties and Fracture Phenomenon of Defected Monolayer Indium Selenide: A Molecular Dynamics Study

In this study, we report the mechanical properties and fracture mechanism of pre-cracked and defected InSe nanosheet samples using molecular dynamics (MD) simulations. We noticed that the failure of pre-cracked and defected InSe nanosheet is governed by brittle type fracture. Armchair directional bonds exhibit a greater resistance for crack propagation relative to the zigzag directional ones. Thus, fracture strength of the pre-cracked sheet is slightly higher for zigzag directional loading than that for armchair. We evaluated the limitation of the applicability of Griffith's criterion for single layer (SL) InSe sheet for nano-cracks as the brittle failure of Griffith prediction demonstrates significant differences with the MD fracture strength. We inspected the effect of temperature on the mechanical properties of the pre-cracked samples of SLInSe. We also discussed the fracture mechanism of both defected and pre-cracked structure at length.

cond-mat.mtrl-sci↗

arXiv2020

Understanding Mechanical Properties and Failure Mechanism of Germanium-Silicon Alloy at Nanoscale

We used molecular dynamics (MD) simulations to investigate the mechanical properties of cubic zinc blende (ZB) Si0.5Ge0.5 alloy nanowire (NW). Tersoff potential is employed to elucidate the effect of nanowire size, crystal orientations, and temperature on the material properties. We found that the reduction in the cross-sectional area results in lower ultimate tensile strength and Youngs modulus of this alloy which can be attributed to the increased surface to volume ratio. The [111] oriented Si0.5Ge0.5 NW exhibits the highest fracture strength compared to other crystal orientations but [110] orientation possesses the highest fracture toughness. The effect of temperature depicts an inverse relationship with the ultimate tensile strength and Youngs modulus. The increased temperature facilitates the failure of the material, thus degrades the materials strength. Our study reveals that the vacancy defects introduced via removal of either Si or Ge atoms exhibit similar behavior, and with the increase in vacancy concentration, both ultimate tensile strength and Youngs modulus reduces linearly. We further illustrate the failure characteristics of Si0.5Ge0.5 NW at two extremely low and high temperatures. The intrinsic failure characteristics of Si0.5Ge0.5 alloy is found to be insensitive to the temperature. Interestingly, at both temperatures, with the increasing strain, the cross-section of Si0.5Ge0.5 eventually resembles a neck as typically observed in ductile materials, although the NW failure is brittle in nature. Overall, this work offers a new perspective on understanding material properties and failure characteristics of ZB Si0.5Ge0.5 NW that will be a guide for designing Si-Ge based nanodevices.

cond-mat.mtrl-sci↗

arXiv2020

Engineered Defects to Modulate Fracture Strength of Single Layer MoS2: An Atomistic Study

We use classical molecular dynamics (MD) simulations to investigate the mechanical properties of pre-cracked, nano-porous single layer MoS2 (SLMoS2) and the effect of interactions between cracks and pores. We found that the failure of pre-cracked and nano-porous SLMoS2 is dominated by brittle type fracture. Bonds in armchair direction show a stronger resistance to crack propagation compared to the zigzag direction. We compared the brittle failure of Griffith prediction with the MD fracture strength and toughness and found substantial differences that limit the applicability of Griffith criterion for SLMoS2 in case of nano-cracks and pores. Next, we demonstrate that the mechanical properties of pre-cracked SLMoS2 can be enhanced via symmetrically placed pores and auxiliary cracks around a central crack and position of such arrangements can be optimized for maximum enhancement of strengths. Such a study would help towards strain engineering based advanced designing of SLMoS2 and other similar Transition Metal Dichalcogenides.

cond-mat.mtrl-sci↗

arXiv2020

Atomistic Investigation on the Mechanical Properties and Failure Behavior of Zinc Blende Cadmium Selenide (CdSe) Nanowire

The mechanical properties of Cadmium Selenide (CdSe) nanowire is an emerging issue due to its application in semiconductor and optoelectronics industries. In this paper, we conducted molecular dynamics (MD) simulations to investigate the temperature-dependent mechanical properties and failure behavior of Zinc-Blende (ZB) CdSe nanowire under uniaxial tensile deformation. We employed Stillinger-Weber (SW) potential to describe the inter-atomic interactions. The effect of variation of temperatures (100 K-600 K), sizes, and crystal orientation on the tensile response of the CdSe nanowires is investigated. Our simulation results suggest that both ultimate tensile strength and Youngs modulus of CdSe have an inverse relationship with temperature. From 100K to 600K, the ZB CdSe exhibits brittle type failure thus there is no brittle to ductile transition temperature found. Results also suggest that size has a significant effect on the mechanical properties of CdSe nanowire. It has been found that as the cross-sectional area increases both ultimate tensile stress and Youngs modulus increases as well. The [111] oriented ZB CdSe shows the largest ultimate tensile strength, Youngs modulus and fracture toughness whereas the values are lowest for [100] orientation. The [110] orientation shows the largest failure strain compared to other orientations. Finally, failure mechanisms of CdSe nanowire are also investigated at 100K and 600K. We noticed that at 100K temperature [100] oriented ZB CdSe fails along {111} cleavage plane however in the case of 600 K temperature, both {111} and {100} planes are activated and cause fracture of CdSe nanowire at lower strain value. This study can guide to design ZB CdSe based solar cell, optoelectronic and semiconductor devices by presenting a comprehensive understanding of the mechanical and fracture characteristics of this nanowire.

cond-mat.mtrl-sci↗

arXiv2020

Functionalized MXenes as Effective Polyselenides Immobilizer for Lithium-Selenium Batteries: A Density Functional Theory (DFT) Study

The practical applications of lithium selenium (Li-Se) batteries are impeded primarily due to the dissolution and migration of higher order polyselenides (Li2Sen) into the electrolyte (known as shuttle effect) and inactive deposition of lower order polyselenides. The high electrical conductivity and mechanical strengths of MXenes make them a suitable candidate to provide adequate anchoring to prevent polyselenides dissolution and improved electrochemical performance. Herein, we used density functional theory (DFT) calculations to understand the binding mechanism of Li2Sen on graphene and surface functionalized Ti3C2 MXenes. We used graphene as reference material to assess Li2Sen binding strengths on functionalized Ti3C2X2 (where X = S, O, F, and Cl). We observed that Ti3C2S2 and Ti3C2O2 exhibit superior anchoring behavior compared to graphene, Ti3C2F2, and Ti3C2Cl2. The calculated Li2Sen adsorption strength provided by S and O terminated Ti3C2 are stronger than the commonly used ether-based electrolyte, which is a requisite for effective suppression of the Li2Sen shuttling. The adsorbed Li2Sen on Ti3C2X2 and graphene retains their structural integrity without a chemical decomposition. The density of states (DOS) analysis exhibits that the conductive behavior of the Ti3C2X2 is preserved even after Li2Sen adsorption, which can stimulate the electrochemical activity of involved Li2Sen chemistry. Based on our unprecedented results, Ti3C2S2 and Ti3C2O2 are found to exhibit superior anchoring behavior for Li2Sen adsorption, which can be leveraged for designing effective selenium-based cathode materials to boost the electrochemical performance of the Li-Se battery system

cond-mat.mtrl-sci↗

arXiv2020

Atomic Scale Insights Into The Mechanical Characteristics of Monolayer 1T-Titanium Disulphide: A Molecular Dynamics Study

In this work, we report on the mechanical responses and fracture behavior of pristine and defected monolayer 1T-Titanium Disulfide using classical molecular dynamics simulation. We investigated the effect of temperature, strain rate and defect ratio on the uniaxial tensile properties in both armchair and zigzag direction. We found that monolayer TiS2 shows isotropic uniaxial tensile properties except for failure strain which is greater in zigzag direction than armchair direction. We also observed a negative correlation of ultimate tensile strength, failure strain and young's modulus with temperature and defect ratio. Results depicts that strain rate has no effect on the young's modulus of monolayer TiS2 but higher strain rate results in higher ultimate tensile strength and failure strain.

cond-mat.mtrl-sci↗

arXiv2020

First-Principles Investigation of Anchoring Behavior of WS2 and WSe2 for Lithium-Sulfur Batteries

The commercial realization of lithium-sulfur (Li-S) batteries is obstructed because of rapid capacity fading due to lithium polysulfides (LiPSs) dissolution into the electrolyte. In order to enhance the efficiency and performance of the Li-S batteries, the transition metal dichalcogenides are reported as promising anchoring materials (AMs) as they could strongly adsorb and effectively suppress the migration of the polysulfides species. Herein, we used first-principles based density functional theory (DFT) calculations to investigate the interactions between AMs such as tungsten dichalcogenides, WX2 (X=S and Se) and the LiPSs. The LiPSs binding behavior of WS2 and WSe2 are found to be quite similar. The calculated adsorption energies of LiPS species indicate that the WX2 possesses moderate binding strength and the binding is facilitated via charge transfer from the polysulfides to the AM. We observe elongation of intramolecular Li-S bonds in LiPS upon their adsorption onto the WX2, however, chemical structures of LiPSs are preserved without decomposition. The calculated density of states indicates the LiPS adsorbed WX2 systems exhibits semiconducting behavior with a slightly lower bandgap compared to the pristine WX2. Overall, our simulation results provide detailed insight into the behavior of WX2 as AMs to suppress the LiPSs migration and henceforth paves the way towards the development of high-performance Li-S batteries.

cond-mat.mtrl-sci↗

arXiv2017

Atomistic Representation of Anomalies in the Failure Behaviour of Nanocrystalline Silicene

Silicene, a 2D analogue of graphene, has spurred a tremendous research interest in the scientific community for its unique properties essential for next generation electronic devices. In this work, for the first time, we present a molecular dynamics (MD) investigation to determine the fracture strength and toughness of nanocrystalline silicene (nc silicene) sheet of varied grain size and pre existing crack length at room temperature. Our results suggest that the transition from an inverse pseudo Hall Petch to a pseudo Hall Petch behavior in nc silicene occurs at a critical grain size of 17.32 nm. This phenomenon is also prevalent in nanocrystalline graphene. However, nc silicene with pre existing cracks exhibits anomalous crack propagation and fracture toughness behaviour. We have observed two distinct types of failure mechanisms (crack sensitive and insensitive failure) and devised the mechanophysical conditions under which they occur. Fracture toughness calculated from both Griffiths theory and MD simulations indicate that the former overpredicts the fracture toughness of nc silicene. The most striking outcome, however, is that despite the presence of a pre existing crack, the crack sensitivity of nc silicene is found to be dependent on the grain size and their orientations. This study is the first direct comparison of atomistic simulations to the continuum theories to predict the anomalous behaviour in deformation and failure mechanisms of nc silicene.

cond-mat.mtrl-sci↗