Nanomaterials

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15 pages, 1520 KiB

Open AccessArticle

Tunable Thermal Transport Characteristics of Nanocomposites

by G. P. Srivastava and Iorwerth O. Thomas

Nanomaterials 2020, 10(4), 673; https://doi.org/10.3390/nano10040673 - 3 Apr 2020

Cited by 3 | Viewed by 1933

We present a study of tunable thermal transport characteristics of nanocomposites by employing a combination of a full-scale semi-ab inito approach and a generalised and extended modification of the effective medium theory. Investigations are made for planar superlattices (PSLs) and nanodot superlattices [...] Read more.

We present a study of tunable thermal transport characteristics of nanocomposites by employing a combination of a full-scale semi-ab inito approach and a generalised and extended modification of the effective medium theory. Investigations are made for planar superlattices (PSLs) and nanodot superlattices (NDSLs) constructed from isotropic conductivity covalent materials Si and Ge, and NDSLs constructed from anisotropic conductivity covalent-van der Waals materials MoS

_{2}

and WS

_{2}

. It is found that difference in the conductivities of individual materials, period size, volume fraction of insertion, and atomic-level interface quality are the four main parameters to control phonon transport in nanocomposite structures. It is argued that the relative importance of these parameters is system dependent. The equal-layer thickness Si/Ge PSL shows a minimum in the room temperature conductivity for the period size of around 4 nm, and with a moderate amount of interface mass smudging this value lies below the conductivity of SiGe alloy. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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13 pages, 8100 KiB

Open AccessArticle

A First-Principles Study of Nonlinear Elastic Behavior and Anisotropic Electronic Properties of Two-Dimensional HfS₂

by Mahdi Faghihnasiri, Aidin Ahmadi, Samaneh Alvankar Golpayegan, Saeideh Garosi Sharifabadi and Ali Ramazani

Nanomaterials 2020, 10(3), 446; https://doi.org/10.3390/nano10030446 - 1 Mar 2020

Cited by 28 | Viewed by 3648

Abstract

We utilize first principles calculations to investigate the mechanical properties and strain-dependent electronic band structure of the hexagonal phase of two dimensional (2D) HfS₂. We apply three different deformation modes within −10% to 30% range of two uniaxial (D1, D2) and [...] Read more.

We utilize first principles calculations to investigate the mechanical properties and strain-dependent electronic band structure of the hexagonal phase of two dimensional (2D) HfS₂. We apply three different deformation modes within −10% to 30% range of two uniaxial (D1, D2) and one biaxial (D3) strains along x, y, and x-y directions, respectively. The harmonic regions are identified in each deformation mode. The ultimate stress for D1, D2, and D3 deformations is obtained as 0.037, 0.038 and 0.044 (eV/Ang3), respectively. Additionally, the ultimate strain for D1, D2, and D3 deformation is obtained as 17.2, 17.51, and 21.17 (eV/Ang3), respectively. In the next step, we determine the second-, third-, and fourth-order elastic constants and the electronic properties of both unstrained and strained HfS₂ monolayers are investigated. Our findings reveal that the unstrained HfS₂ monolayer is a semiconductor with an indirect bandgap of 1.12 eV. We then tune the bandgap of HfS₂ with strain engineering. Our findings reveal how to tune and control the electronic properties of HfS₂ monolayer with strain engineering, and make it a potential candidate for a wide range of applications including photovoltaics, electronics and optoelectronics. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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12 pages, 20468 KiB

Open AccessArticle

Electro-Optical Properties of Monolayer and Bilayer Pentagonal BN: First Principles Study

by Mehran Amiri, Javad Beheshtian, Farzaneh Shayeganfar, Mahdi Faghihnasiri, Rouzbeh Shahsavari and Ali Ramazani

Nanomaterials 2020, 10(3), 440; https://doi.org/10.3390/nano10030440 - 29 Feb 2020

Cited by 22 | Viewed by 4153

Abstract

Two-dimensional hexagonal boron nitride (hBN) is an insulator with polar covalent B-N bonds. Monolayer and bilayer pentagonal BN emerge as an optoelectronic material, which can be used in photo-based devices such as photodetectors and photocatalysis. Herein, we implement spin polarized electron density calculations [...] Read more.

Two-dimensional hexagonal boron nitride (hBN) is an insulator with polar covalent B-N bonds. Monolayer and bilayer pentagonal BN emerge as an optoelectronic material, which can be used in photo-based devices such as photodetectors and photocatalysis. Herein, we implement spin polarized electron density calculations to extract electronic/optical properties of mono- and bilayer pentagonal BN structures, labeled as

B_{2} N_{4}

,

B_{3} N_{3}

, and

B_{4} N_{2}

. Unlike the insulating hBN, the pentagonal BN exhibits metallic or semiconducting behavior, depending on the detailed pentagonal structures. The origin of the metallicity is attributed to the delocalized boron (B) 2p electrons, which has been verified by electron localized function and electronic band structure as well as density of states. Interestingly, all 3D networks of different bilayer pentagonal BN are dynamically stable unlike 2D structures, whose monolayer

B_{4} N_{2}

is unstable. These 3D materials retain their metallic and semiconductor nature. Our findings of the optical properties indicate that pentagonal BN has a visible absorption peak that is suitable for photovoltaic application. Metallic behavior of pentagonal BN has a particular potential for thin-film based devices and nanomaterial engineering. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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13 pages, 3398 KiB

Open AccessArticle

New Insight on Hydrogen Evolution Reaction Activity of MoP₂ from Theoretical Perspective

by Yuyue Gao, Hongyan Li, Jingyu Wang, Jianyi Ma and Haisheng Ren

Nanomaterials 2019, 9(9), 1270; https://doi.org/10.3390/nano9091270 - 5 Sep 2019

Cited by 12 | Viewed by 3342

Abstract

We systematically investigated the hydrogen evolution reaction (HER) of six facets of

{MoP}_{2}

based on the periodic density functional theory (DFT). The calculated values of Gibbs free energy of hydrogen adsorption (

Δ G_{H}

) indicated that the (111) facet has [...] Read more.

We systematically investigated the hydrogen evolution reaction (HER) of six facets of

{MoP}_{2}

based on the periodic density functional theory (DFT). The calculated values of Gibbs free energy of hydrogen adsorption (

Δ G_{H}

) indicated that the (111) facet has a good HER activity for a large range of hydrogen coverages. The zigzagged patterns before 75% hydrogen coverage suggest a facilitation among Mo1, P1 and Mo2 sites, which are attributed to repeat occupancy sites of H atoms. From ab initial atomistic thermodynamics analysis of hydrogen coverage, we gained that the most stable coverage of hydrogen is 18.75% at 1 atm

H_{2}

and 298 K. Finally, the doping effects on HER activity were investigated and found that catalytic performance can be improved by substituting P with an S or N atom, as well as substituting the Mo atom with an Fe atom, respectively. We hope this work can provide new insights on further understanding of HER for

{MoP}_{2}

and give instructions for the experimental design and synthesis of transition metal phosphides (TMPs)-based high-performance catalysts. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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11 pages, 2584 KiB

Open AccessArticle

Interaction in Li@Fullerenes and Li⁺@Fullerenes: First Principle Insights to Li-Based Endohedral Fullerenes

by Hongcun Bai, Hongfeng Gao, Wei Feng, Yaping Zhao and Yuhua Wu

Nanomaterials 2019, 9(4), 630; https://doi.org/10.3390/nano9040630 - 18 Apr 2019

Cited by 25 | Viewed by 4247

Abstract

This work reveals first principle results of the endohedral fullerenes made from neutral or charged single atomic lithium (Li or Li⁺) encapsulated in fullerenes with various cage sizes. According to the calculated binding energies, it is found that the encapsulation of [...] Read more.

This work reveals first principle results of the endohedral fullerenes made from neutral or charged single atomic lithium (Li or Li⁺) encapsulated in fullerenes with various cage sizes. According to the calculated binding energies, it is found that the encapsulation of a single lithium atom is energetically more favorable than that of lithium cation. Lithium, in both atomic and cationic forms, exhibits a clear tendency to depart from the center in large cages. Interaction effects dominate the whole encapsulation process of lithium to carbon cages. Further, the nature of the interaction between Li (or Li⁺) and carbon cages is discussed based on reduced density gradient, energy decomposition analysis, and charge transfer. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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9 pages, 1713 KiB

Open AccessArticle

Molecular Dynamics Calculations of Grain Boundary Mobility in CdTe

by Rodolfo Aguirre, Sharmin Abdullah, Xiaowang Zhou and David Zubia

Nanomaterials 2019, 9(4), 552; https://doi.org/10.3390/nano9040552 - 4 Apr 2019

Cited by 5 | Viewed by 4206

Abstract

Molecular dynamics (MD) simulations have been applied to study mobilities of Σ3, Σ7 and Σ11 grain boundaries in CdTe. First, an existing MD approach to drive the motion of grain boundaries in face-centered-cubic and body-centered-cubic crystals was generalized for arbitrary crystals. MD simulations [...] Read more.

Molecular dynamics (MD) simulations have been applied to study mobilities of Σ3, Σ7 and Σ11 grain boundaries in CdTe. First, an existing MD approach to drive the motion of grain boundaries in face-centered-cubic and body-centered-cubic crystals was generalized for arbitrary crystals. MD simulations were next performed to calculate grain boundary velocities in CdTe crystals at different temperatures, driving forces, and grain boundary terminations. Here a grain boundary is said to be Te-terminated if its migration encounters sequentially

C d \cdot T e - C d \cdot T e

… planes, where “·” and “−” represent short and long spacing respectively. Likewise, a grain boundary is said to be Cd-terminated if its migration encounters sequentially

T e \cdot C d - T e \cdot C d

… planes. Grain boundary mobility laws, suitable for engineering time and length scales, were then obtained by fitting the MD results to Arrhenius equation. These studies indicated that the Σ3 grain boundary has significantly lower mobility than the Σ7 and Σ11 grain boundaries. The Σ7 Te-terminated grain boundary has lower mobility than the Σ7 Cd-terminated grain boundary, and that the Σ11 Cd-terminated grain boundary has lower mobility than the Σ11 Te-terminated grain boundary. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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13 pages, 1606 KiB

Open AccessArticle

Computational Screening of Metal–Organic Framework Membranes for the Separation of 15 Gas Mixtures

by Wenyuan Yang, Hong Liang, Feng Peng, Zili Liu, Jie Liu and Zhiwei Qiao

Nanomaterials 2019, 9(3), 467; https://doi.org/10.3390/nano9030467 - 20 Mar 2019

Cited by 34 | Viewed by 4959

Abstract

The Monte Carlo and molecular dynamics simulations are employed to screen the separation performance of 6013 computation-ready, experimental metal–organic framework membranes (CoRE-MOFMs) for 15 binary gas mixtures. After the univariate analysis, principal component analysis is used to reduce 44 performance metrics of 15 [...] Read more.

The Monte Carlo and molecular dynamics simulations are employed to screen the separation performance of 6013 computation-ready, experimental metal–organic framework membranes (CoRE-MOFMs) for 15 binary gas mixtures. After the univariate analysis, principal component analysis is used to reduce 44 performance metrics of 15 mixtures to a 10-dimension set. Then, four machine learning algorithms (decision tree, random forest, support vector machine, and back propagation neural network) are combined with k times repeated k-fold cross-validation to predict and analyze the relationships between six structural feature descriptors and 10 principal components. Based on the linear correlation value R and the root mean square error predicted by the machine learning algorithm, the random forest algorithm is the most suitable for the prediction of the separation performance of CoRE-MOFMs. One descriptor, pore limiting diameter, possesses the highest weight importance for each principal component index. Finally, the 30 best CoRE-MOFMs for each binary gas mixture are screened out. The high-throughput computational screening and the microanalysis of high-dimensional performance metrics can provide guidance for experimental research through the relationships between the multi-structure variables and multi-performance variables. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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15 pages, 5436 KiB

Open AccessArticle

Reactivity of Atomically Functionalized C-Doped Boron Nitride Nanoribbons and Their Interaction with Organosulfur Compounds

by Francisco Villanueva-Mejia, Pedro Navarro-Santos, Peter Ludwig Rodríguez-Kessler, Rafael Herrera-Bucio and José Luis Rivera

Nanomaterials 2019, 9(3), 452; https://doi.org/10.3390/nano9030452 - 18 Mar 2019

Cited by 9 | Viewed by 2961

Abstract

The electronic and reactivity properties of carbon doped (C-doped) boron nitride nanoribbons (BNNRs) as a function of the carbon concentration were investigated in the framework of the density functional theory within the generalized gradient approximation. We found that the main routes to stabilize [...] Read more.

The electronic and reactivity properties of carbon doped (C-doped) boron nitride nanoribbons (BNNRs) as a function of the carbon concentration were investigated in the framework of the density functional theory within the generalized gradient approximation. We found that the main routes to stabilize energetically the C-doped BNNRs involve substituting boron atoms near the edges. However, the effect of doping on the electronic properties depends of the sublattice where the C atoms are located; for instance, negative doping (partial occupations of electronic states) is found replacing B atoms, whereas positive doping (partial inoccupation of electronic states) is found when replacing N atoms with respect to the pristine BNNRs. Independently of the even or odd number of dopants of the C-doped BNNRs studied in this work, the solutions of the Kohn Sham equations suggest that the most stable solution is the magnetic one. The reactivity of the C-doped BNNRs is inferred from results of the dual descriptor, and it turns out that the main electrophilic sites are located near the dopants along the C-doped BNNRs. The reactivity of these nanostructures is tested by calculating the interaction energy between undesirable organosulfur compounds present in oil fuels on the C-doped BNNRs, finding that organosulfur compounds prefer to interact over nanosurfaces with dopants substituted on the B sublattice of the C-doped BNNRs. Most importantly, the selective C doping on the BNNRs offers the opportunity to tune the properties of the BNNRs to fit novel technological applications. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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31 pages, 8672 KiB

Open AccessArticle

Structure and Electronic Properties of TiO₂ Nanoclusters and Dye–Nanocluster Systems Appropriate to Model Hybrid Photovoltaic or Photocatalytic Applications

by Corneliu I. Oprea and Mihai A. Gîrțu

Nanomaterials 2019, 9(3), 357; https://doi.org/10.3390/nano9030357 - 4 Mar 2019

Cited by 31 | Viewed by 4212

Abstract

We report the results of a computational study of TiO₂ nanoclusters of various sizes as well as of complex systems with various molecules adsorbed onto the clusters to set the ground for the modeling of charge transfer processes in hybrid organic–inorganic photovoltaics [...] Read more.

We report the results of a computational study of TiO₂ nanoclusters of various sizes as well as of complex systems with various molecules adsorbed onto the clusters to set the ground for the modeling of charge transfer processes in hybrid organic–inorganic photovoltaics or photocatalytic degradation of pollutants. Despite the large number of existing computational studies of TiO₂ clusters and in spite of the higher computing power of the typical available hardware, allowing for calculations of larger systems, there are still studies that use cluster sizes that are too small and not appropriate to address particular problems or certain complex systems relevant in photovoltaic or photocatalytic applications. By means of density functional theory (DFT) calculations, we attempt to find acceptable minimal sizes of the Ti_nO_2n+2H₄ (n = 14, 24, 34, 44, 54) nanoclusters in correlation with the size of the adsorbed molecule and the rigidity of the backbone of the molecule to model systems and interface processes that occur in hybrid photovoltaics and photocatalysis. We illustrate various adsorption cases with a small rigid molecule based on coumarin, a larger rigid oligomethine cyanine dye with indol groups, and the penicillin V antibiotic having a flexible backbone. We find that the use of the n = 14 cluster to describe adsorption leads to significant distortions of both the cluster and the molecule and to unusual tridentate binding configurations not seen for larger clusters. Moreover, the significantly weaker bonding as well as the differences in the density of states and in the optical spectra suggest that the n = 14 cluster is a poor choice for simulating the materials used in the practical applications envisaged here. As the n = 24 cluster has provided mixed results, we argue that cluster sizes larger than or equal to n = 34 are necessary to provide the reliability required by photovoltaic and photocatalytic applications. Furthermore, the tendency to saturate the key quantities of interest when moving from n = 44 to n = 54 suggests that the largest cluster may bring little improvement at a significantly higher computational cost. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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14 pages, 2551 KiB

Open AccessArticle

Computational Investigation of Tuning the Electron-Donating Ability in Metal-Free Organic Dyes Featuring an Azobenzene Spacer for Dye-Sensitized Solar Cells

by Md Al Mamunur Rashid, Dini Hayati, Kyungwon Kwak and Jongin Hong

Nanomaterials 2019, 9(1), 119; https://doi.org/10.3390/nano9010119 - 18 Jan 2019

Cited by 15 | Viewed by 5472

Abstract

A series of donor–π-conjugated spacer–acceptor (D–π–A) organic dyes featuring an azobenzene spacer were designed as chromic dyes and investigated computationally. The electron-donating strength was modified by introducing electron-donating units to the donor side. In particular, the trans–cis isomerization of the azobenzene-based [...] Read more.

A series of donor–π-conjugated spacer–acceptor (D–π–A) organic dyes featuring an azobenzene spacer were designed as chromic dyes and investigated computationally. The electron-donating strength was modified by introducing electron-donating units to the donor side. In particular, the trans–cis isomerization of the azobenzene-based dyes and its effect on the optical and electronic properties were further scrutinized. In both trans and cis conformers, a gradual increase in electron-donating strength promoted the natural charge separation between donor and acceptor moieties, thereby allowing the absorption of a longer wavelength of visible light. Importantly, the conformational change of the azobenzene bridge resulted in different absorption spectra and light-harvesting properties. The azobenzene-based dyes will open up a new research path for chromic dye-sensitized solar cells. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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10 pages, 4307 KiB

Open AccessArticle

First-Principles Study on the Stabilities, Electronic and Optical Properties of Ge_xSn_1-xSe Alloys

by Qi Qian, Lei Peng, Yu Cui, Liping Sun, Jinyan Du and Yucheng Huang

Nanomaterials 2018, 8(11), 876; https://doi.org/10.3390/nano8110876 - 25 Oct 2018

Cited by 1 | Viewed by 3464

Abstract

We systematically study, by using first-principles calculations, stabilities, electronic properties, and optical properties of Ge_xSn_1-xSe alloy made of SnSe and GeSe monolayers with different Ge concentrations x = 0.0, 0.25, 0.5, 0.75, and 1.0. Our results show that the [...] Read more.

We systematically study, by using first-principles calculations, stabilities, electronic properties, and optical properties of Ge_xSn_1-xSe alloy made of SnSe and GeSe monolayers with different Ge concentrations x = 0.0, 0.25, 0.5, 0.75, and 1.0. Our results show that the critical solubility temperature of the alloy is around 580 K. With the increase of Ge concentration, band gap of the alloy increases nonlinearly and ranges from 0.92 to 1.13 eV at the PBE level and 1.39 to 1.59 eV at the HSE06 level. When the Ge concentration x is more than 0.5, the alloy changes into a direct bandgap semiconductor; the band gap ranges from 1.06 to 1.13 eV at the PBE level and 1.50 to 1.59 eV at the HSE06 level, which falls within the range of the optimum band gap for solar cells. Further optical calculations verify that, through alloying, the optical properties can be improved by subtle controlling the compositions. Since Ge_xSn_1-xSe alloys with different compositions have been successfully fabricated in experiments, we hope these insights will contribute to the future application in optoelectronics. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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15 pages, 6272 KiB

Open AccessArticle

Tailoring Bandgap of Perovskite BaTiO₃ by Transition Metals Co-Doping for Visible-Light Photoelectrical Applications: A First-Principles Study

by Fan Yang, Liang Yang, Changzhi Ai, Pengcheng Xie, Shiwei Lin, Cai-Zhuang Wang and Xihong Lu

Nanomaterials 2018, 8(7), 455; https://doi.org/10.3390/nano8070455 - 21 Jun 2018

Cited by 49 | Viewed by 6441

Abstract

The physical and chemical properties of V-M″ and Nb-M″ (M″ is 3d or 4d transition metal) co-doped BaTiO₃ were studied by first-principles calculation based on density functional theory. Our calculation results show that V-M″ co-doping is more favorable than Nb-M″ co-doping in [...] Read more.

The physical and chemical properties of V-M″ and Nb-M″ (M″ is 3d or 4d transition metal) co-doped BaTiO₃ were studied by first-principles calculation based on density functional theory. Our calculation results show that V-M″ co-doping is more favorable than Nb-M″ co-doping in terms of narrowing the bandgap and increasing the visible-light absorption. In pure BaTiO₃, the bandgap depends on the energy levels of the Ti 3d and O 2p states. The appropriate co-doping can effectively manipulate the bandgap by introducing new energy levels interacting with those of the pure BaTiO₃. The optimal co-doping effect comes from the V-Cr co-doping system, which not only has smaller impurity formation energy, but also significantly reduces the bandgap. Detailed analysis of the density of states, band structure, and charge-density distribution in the doping systems demonstrates the synergistic effect induced by the V and Cr co-doping. The results can provide not only useful insights into the understanding of the bandgap engineering by element doping, but also beneficial guidance to the experimental study of BaTiO₃ for visible-light photoelectrical applications. Full article

(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)

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