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17 pages, 4906 KiB

Open AccessEditor’s ChoiceArticle

Sensing at the Nanoscale Using Nitrogen-Vacancy Centers in Diamond: A Model for a Quantum Pressure Sensor

by Hari P. Paudel, Gary R. Lander, Scott E. Crawford and Yuhua Duan

Nanomaterials 2024, 14(8), 675; https://doi.org/10.3390/nano14080675 - 12 Apr 2024

Viewed by 1943

Abstract

The sensing of stress under harsh environmental conditions with high resolution has critical importance for a range of applications including earth’s subsurface scanning, geological CO₂ storage monitoring, and mineral and resource recovery. Using a first-principles density functional theory (DFT) approach combined with [...] Read more.

The sensing of stress under harsh environmental conditions with high resolution has critical importance for a range of applications including earth’s subsurface scanning, geological CO₂ storage monitoring, and mineral and resource recovery. Using a first-principles density functional theory (DFT) approach combined with the theoretical modelling of the low-energy Hamiltonian, here, we investigate a novel approach to detect unprecedented levels of pressure by taking advantage of the solid-state electronic spin of nitrogen-vacancy (NV) centers in diamond. We computationally explore the effect of strain on the defect band edges and band gaps by varying the lattice parameters of a diamond supercell hosting a single NV center. A low-energy Hamiltonian is developed that includes the effect of stress on the energy level of a ±1 spin manifold at the ground state. By quantifying the energy level shift and split, we predict pressure sensing of up to 0.3 MPa/

\sqrt{Hz}

using the experimentally measured spin dephasing time. We show the superiority of the quantum sensing approach over traditional optical sensing techniques by discussing our results from DFT and theoretical modelling for the frequency shift per unit pressure. Importantly, we propose a quantum manometer that could be useful to measure earth’s subsurface vibrations as well as for pressure detection and monitoring in high-temperature superconductivity studies and in material sciences. Our results open avenues for the development of a sensing technology with high sensitivity and resolution under extreme pressure limits that potentially has a wider applicability than the existing pressure sensing technologies. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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12 pages, 2529 KiB

Open AccessArticle

First-Principles Investigation of Simultaneous Thermoelectric Power Generation and Active Cooling in a Bifunctional Semimetal ZrSeTe Janus Structure

by Brahim Marfoua and Jisang Hong

Nanomaterials 2024, 14(2), 234; https://doi.org/10.3390/nano14020234 - 22 Jan 2024

Viewed by 1181

Abstract

Traditional thermoelectric materials often face a trade-off between efficient power generation (high ZT) and cooling performance. Here, we explore the potential of achieving simultaneous thermoelectric power generation and cooling capability in the recently fabricated bulk ZrSeTe Janus structure using first-principles density functional theory [...] Read more.

Traditional thermoelectric materials often face a trade-off between efficient power generation (high ZT) and cooling performance. Here, we explore the potential of achieving simultaneous thermoelectric power generation and cooling capability in the recently fabricated bulk ZrSeTe Janus structure using first-principles density functional theory (DFT). The layered ZrSeTe Janus structure exhibits a semimetal character with anisotropic transport properties along the in-plane and out-of-plane directions. Our DFT calculations, including the explicit calculation of relaxation time, reveal a maximum ZT of ~0.065 in the out-of-plane direction at 300 K which is one order of magnitude larger than that in the in-plane direction (ZT~0.006). Furthermore, the thermoelectric cooling performance is also investigated. The in-plane direction shows a cooling performance of 13 W/m·K and a coefficient of performance (COP_max) of ~90 with a temperature difference (ΔT) of 30 K, while the out-of-plane direction has a cooling performance of 2.5 W/m·K and COP_max of ~2.5. Thus, the out-of-plane current from the thermoelectric power generation can be utilized as an in-plane current source for active heat pumping. Consequently, we propose that the semimetal ZrSeTe Janus structure can display bifunctional thermoelectric properties for simultaneous thermoelectric power generation and active cooling. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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19 pages, 2860 KiB

Open AccessArticle

Effect of Zwitterionic Additives on Solvation and Transport of Sodium and Potassium Cations in (Ethylene Oxide)₁₀: A Molecular Dynamics Simulation Study

by Manh Tien Nguyen, Yuhua Duan and Qing Shao

Nanomaterials 2024, 14(2), 219; https://doi.org/10.3390/nano14020219 - 19 Jan 2024

Cited by 2 | Viewed by 1205

Abstract

Sodium- (Na⁺) and potassium- (K⁺) ion batteries are cost-effective alternatives to lithium-ion (Li⁺) batteries due to the abundant sodium and potassium resources. Solid polymer electrolytes (SPEs) are essential for safer and more efficient Na⁺ and K [...] Read more.

Sodium- (Na⁺) and potassium- (K⁺) ion batteries are cost-effective alternatives to lithium-ion (Li⁺) batteries due to the abundant sodium and potassium resources. Solid polymer electrolytes (SPEs) are essential for safer and more efficient Na⁺ and K⁺ batteries because they often exhibit low ionic conductivity at room temperature. While zwitterionic (ZW) materials enhance Li⁺ battery conductivity, their potential for Na⁺ and K⁺ transport in batteries remains unexplored. In this study, we investigated the effect of three ZW molecules (ChoPO4, i.e., 2-methacryloyloxyethyl phosphorylcholine, ImSO3, i.e., sulfobetaine ethylimidazole, and ImCO2, i.e., carboxybetaine ethylimidazole) on the dissociation of Na⁺ and K⁺ coordination with ethylene oxide (EO) chains in EO-based electrolytes through molecular dynamics simulations. Our results showed that ChoPO4 possessed the highest cation–EO₁₀ dissociation ability, while ImSO3 exhibited the lowest. Such dissociation ability correlated with the cation–ZW molecule coordination strength: ChoPO4 and ImSO3 showed the strongest and the weakest coordination with cations. However, the cation–ZW molecule coordination could slow the cationic diffusion. The competition of these effects resulted in accelerating or decelerating cationic diffusion. Our simulated results showed that ImCO2 enhanced Na⁺ diffusion by 20%, while ChoPO4 and ImSO3 led to a 10% reduction. For K⁺, ChoPO4 reduced its diffusion by 40%, while ImCO2 and ImSO3 caused a similar decrease of 15%. These findings suggest that the ZW structure and the cationic size play an important role in the ionic dissociation effect of ZW materials. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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10 pages, 3959 KiB

Open AccessCommunication

Electronic Structures of Kitaev Magnet Candidates RuCl₃ and RuI₃

by Subhasis Samanta, Dukgeun Hong and Heung-Sik Kim

Nanomaterials 2024, 14(1), 9; https://doi.org/10.3390/nano14010009 - 19 Dec 2023

Cited by 2 | Viewed by 1376

Abstract

Layered honeycomb magnets with strong atomic spin–orbit coupling at transition metal sites have been intensively studied for the search of Kitaev magnetism and the resulting non-Abelian braiding statistics.

α

-RuCl

_{3}

has been the most promising candidate, and there have been several reports [...] Read more.

Layered honeycomb magnets with strong atomic spin–orbit coupling at transition metal sites have been intensively studied for the search of Kitaev magnetism and the resulting non-Abelian braiding statistics.

α

-RuCl

_{3}

has been the most promising candidate, and there have been several reports on the realization of sibling compounds

α

-RuBr

_{3}

and

α

-RuI

_{3}

with the same crystal structure. Here, we investigate correlated electronic structures of

α

-RuCl

_{3}

and

α

-RuI

_{3}

by employing first-principles dynamical mean-field theory. Our result provides a valuable insight into the discrepancy between experimental and theoretical reports on transport properties of

α

-RuI

_{3}

, and suggests a potential realization of correlated flat bands with strong spin–orbit coupling and a quantum spin-Hall insulating phase in

α

-RuI

_{3}

. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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14 pages, 6598 KiB

Open AccessArticle

Hole-Doping-Induced Perpendicular Magnetic Anisotropy and High Curie Temperature in a CrSX (X = Cl, Br, I) Semiconductor Monolayer

by Ruilin Han, Xiaomin Xue and Yu Yan

Nanomaterials 2023, 13(24), 3105; https://doi.org/10.3390/nano13243105 - 8 Dec 2023

Cited by 1 | Viewed by 1754

Abstract

A large perpendicular magnetic anisotropy and a high Curie temperature (T_C) are crucial for the application of two-dimensional (2D) intrinsic ferromagnets to spintronic devices. Here, we investigated the electronic and magnetic properties of carrier-doped Van der Waals layered CrSX (X = [...] Read more.

A large perpendicular magnetic anisotropy and a high Curie temperature (T_C) are crucial for the application of two-dimensional (2D) intrinsic ferromagnets to spintronic devices. Here, we investigated the electronic and magnetic properties of carrier-doped Van der Waals layered CrSX (X = Cl, Br, I) ferromagnets using first-principles calculations. It was found that hole doping can increase the magnitude of the magnetic anisotropy energy (MAE) and change the orientation of the easy magnetization axis at small doping amounts of 2.37 × 10¹³, 3.98 × 10¹², and 3.33 × 10¹²/cm² for CrSCl, CrSBr, and CrSI monolayers, respectively. The maximum values of the MAE reach 57, 133, and 1597 μeV/u.c. for the critical hole-doped CrSCl, CrSBr, and CrSI with spin orientation along the (001) direction, respectively. Furthermore, the Fermi energy level of lightly hole-doped CrSX (X = Cl, Br, I) moves into the spin-up valence band, leading to the CrSX (X = Cl, Br, I) magnetic semiconductor monolayer becoming first a half-metal and then a metal. In addition, the T_C can also be increased up to 305, 317, and 345 K for CrSCl, CrSBr, and CrSI monolayers at doping amounts of 5.94 × 10¹⁴, 5.78 × 10¹⁴, and 5.55 × 10¹⁴/cm², respectively. These properties suggest that the hole-doping process can render 2D CrSX (X = Cl, Br, I) monolayers remarkable materials for application to electrically controlled spintronic devices. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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13 pages, 2269 KiB

Open AccessArticle

First-Principles Dynamics Investigation of Germanium as an Anode Material in Multivalent-Ion Batteries

by Chaewon Kim, Useul Hwang, Sangjin Lee and Young-Kyu Han

Nanomaterials 2023, 13(21), 2868; https://doi.org/10.3390/nano13212868 - 30 Oct 2023

Cited by 1 | Viewed by 1705

Abstract

Germanium, a promising electrode material for high-capacity lithium ion batteries (LIBs) anodes, attracted much attention because of its large capacity and remarkably fast charge/discharge kinetics. Multivalent-ion batteries are of interest as potential alternatives to LIBs because they have a higher energy density and [...] Read more.

Germanium, a promising electrode material for high-capacity lithium ion batteries (LIBs) anodes, attracted much attention because of its large capacity and remarkably fast charge/discharge kinetics. Multivalent-ion batteries are of interest as potential alternatives to LIBs because they have a higher energy density and are less prone to safety hazards. In this study, we probed the potential of amorphous Ge anodes for use in multivalent-ion batteries. Although alloying Al and Zn in Ge anodes is thermodynamically unstable, Mg and Ca alloys with Ge form stable compounds, Mg_2.3Ge and Ca_2.4Ge that exhibit higher capacities than those obtained by alloying Li, Na, or K with Ge, corresponding to 1697 and 1771 mA·h·g^–1, respectively. Despite having a slightly lower capacity than Ca–Ge, Mg–Ge shows an approximately 150% smaller volume expansion ratio (231% vs. 389%) and three orders of magnitude higher ion diffusivity (3.0 × 10⁻⁸ vs. 1.1 × 10⁻¹¹ cm² s⁻¹) than Ca–Ge. Furthermore, ion diffusion in Mg–Ge occurs at a rate comparable to that of monovalent ions, such as Li⁺, Na⁺, and K⁺. The outstanding performance of the Mg–Ge system may originate from the coordination number of the Ge host atoms and the smaller atomic size of Mg. Therefore, Ge anodes could be applied in multivalent-ion batteries using Mg²⁺ as the carrier ion because its properties can compete with or surpass monovalent ions. Here, we report that the maximum capacity, volume expansion ratio, and ion diffusivities of the alloying electrode materials can be understood using atomic-scale structural properties, such as the host–host and host–ion coordination numbers, as valuable indicators. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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15 pages, 10599 KiB

Open AccessArticle

DFT Study of Zn-Modified SnP₃: A H₂S Gas Sensor with Superior Sensitivity, Selectivity, and Fast Recovery Time

by Hongyuan Cui, Chenshan Gao, Pengwei Wang, Lijie Li, Huaiyu Ye, Zhongquan Wen and Yufei Liu

Nanomaterials 2023, 13(20), 2781; https://doi.org/10.3390/nano13202781 - 17 Oct 2023

Cited by 5 | Viewed by 1983

Abstract

The adsorption properties of Cu, Ag, Zn, and Cd-modified SnP₃ monolayers for H₂S have been studied using density functional theory (DFT). Based on phonon spectrum calculations, a structurally stable intrinsic SnP₃ monolayer was obtained, based on which four metal-modified [...] Read more.

The adsorption properties of Cu, Ag, Zn, and Cd-modified SnP₃ monolayers for H₂S have been studied using density functional theory (DFT). Based on phonon spectrum calculations, a structurally stable intrinsic SnP₃ monolayer was obtained, based on which four metal-modified SnP₃ monolayers were constructed, and the band gaps of the modified SnP₃ monolayers were significantly reduced. The adsorption capacity of Cu, Zn-modified SnP₃ was better than that of Ag, Cd-modified SnP₃. The adsorption energies of Cu-modified SnP₃ and Zn-modified SnP₃ for H₂S were −0.749 eV and −0.639 eV, respectively. In addition, Cu-modified SnP₃ exhibited chemisorption for H₂S, while Zn-modified SnP₃ exhibited strong physisorption, indicating that it can be used as a sensor substrate. Co-adsorption studies showed that ambient gases such as N₂, O₂, and H₂O had little effect on H₂S. The band gap change rate of Zn-modified SnP₃ after adsorption of H₂S was as high as −28.52%. Recovery time studies based on Zn-modified SnP₃ showed that the desorption time of H₂S was 0.064 s at 298 K. Therefore, Zn-modified SnP₃ can be used as a promising sensor substrate for H₂S due to its good selectivity, sensitivity, and fast recovery time. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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9 pages, 1925 KiB

Open AccessArticle

First-Principles Investigation of Size Effects on Cohesive Energies of Transition-Metal Nanoclusters

by Amogh Vig, Ethan Doan and Kesong Yang

Nanomaterials 2023, 13(16), 2356; https://doi.org/10.3390/nano13162356 - 17 Aug 2023

Cited by 5 | Viewed by 2935

Abstract

The cohesive energy of transition-metal nanoparticles is crucial to understanding their stability and fundamental properties, which are essential for developing new technologies and applications in fields such as catalysis, electronics, energy storage, and biomedical engineering. In this study, we systematically investigate the size-dependent [...] Read more.

The cohesive energy of transition-metal nanoparticles is crucial to understanding their stability and fundamental properties, which are essential for developing new technologies and applications in fields such as catalysis, electronics, energy storage, and biomedical engineering. In this study, we systematically investigate the size-dependent cohesive energies of all the 3d, 4d, and 5d transition-metal nanoclusters (small nanoparticles) based on a plane-wave-based method within general gradient approximation using first-principles density functional theory calculations. Our results show that the cohesive energies of nanoclusters decrease with decreasing size due to the increased surface-to-volume ratio and quantum confinement effects. A comparison of nanoclusters with different geometries reveals that the cohesive energy decreases as the number of nanocluster layers decreases. Notably, monolayer nanoclusters exhibit the lowest cohesive energies. We also find that the size-dependent cohesive energy trends are different for different transition metals, with some metals exhibiting stronger size effects than others. Our findings provide insights into the fundamental properties of transition-metal nanoclusters and have potential implications for their applications in various fields, such as catalysis, electronics, and biomedical engineering. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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11 pages, 972 KiB

Open AccessArticle

Strain-Induced Structural Phase Transitions in Epitaxial (001) BiCoO₃ Films: A First-Principles Study

by Hao Tian, Shuqi Cui, Long Fu, Hongwei Zhang, Chenggang Li, Yingqi Cui and Aijie Mao

Nanomaterials 2023, 13(16), 2342; https://doi.org/10.3390/nano13162342 - 15 Aug 2023

Cited by 1 | Viewed by 1057

Abstract

We have simulated BiCoO

_{3}

films epitaxially grown along (001) direction with density functional theory computations. Leading candidates for the lowest-energy phases have been identified. The tensile strains induce magnetic phase transition in the ground state (

P 4 m m

symmetry) from [...] Read more.

We have simulated BiCoO

_{3}

films epitaxially grown along (001) direction with density functional theory computations. Leading candidates for the lowest-energy phases have been identified. The tensile strains induce magnetic phase transition in the ground state (

P 4 m m

symmetry) from a C-type antiferromagnetic order to a G-type order for the in-plane lattice parameter above 3.922 Å. The G-type antiferromagnetic order will be maintained with larger tensile strains; however, a continuous structural phase transition will occur, combining the ferroelectric and antiferrodistortive modes. In particular, the larger tensile strain allows an isostructural transition, the so-called Cowley’s ‘‘Type Zero’’ phase transitions, from

C c

-(I) to

C c

-(II), with a slight volume collapse. The orientation of ferroelectric polarization changes from the out-of-plane direction in the

P 4 m m

to the in-plane direction in the

P m c 2_{1}

state under epitaxial tensile strain; meanwhile, the magnetic ordering temperature T

_{N}

can be strikingly affected by the variation of misfit strain. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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12 pages, 1928 KiB

Open AccessArticle

Electronic Characteristics, Stability and Water Oxidation Selectivity of High-Index BiVO₄ Facets for Photocatalytic Application: A First Principle Study

by Zhiyuan Zhang, Yuqi Xiang and Zhihong Zhu

Nanomaterials 2023, 13(13), 2023; https://doi.org/10.3390/nano13132023 - 7 Jul 2023

Cited by 1 | Viewed by 1407

Abstract

Some high-index facets of BiVO₄, such as (012), (210), (115), (511), (121), (132) and (231), exhibit much better photocatalytic performance than conventional (010) and (110) surfaces for water splitting. However, the detailed mechanisms and stability of improved photocatalytic performance for these [...] Read more.

Some high-index facets of BiVO₄, such as (012), (210), (115), (511), (121), (132) and (231), exhibit much better photocatalytic performance than conventional (010) and (110) surfaces for water splitting. However, the detailed mechanisms and stability of improved photocatalytic performance for these high-index BiVO₄ surfaces are still not clear, which is important for designing photocatalysts with high efficiency. Here, based on first principle calculation, we carried out a systematic theoretical research on BiVO₄ with different surfaces, especially high-index facets. The results show that all of the high-index facets in our calculated systems show an n-type behavior, and the band edge positions indicate that all of the high-index facets have enough ability to produce O₂ without external bias. Electronic structures, band alignments and formation enthalpy indicate that (012), (115) and (132) could be equivalent to (210), (511) and (231), respectively, in the calculation. Oxidation and reduction potential show that only (132)/(231) is stable without strongly oxidative conditions, and the Gibbs free energy indicates that (012)/(210), (115)/(511), (121) and (132)/(231) have lower overpotential than (010) and (110). Our calculation is able to unveil insights into the effects of the surface, including electronic structures, overpotential and stability during the reaction process. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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18 pages, 25736 KiB

Open AccessEditor’s ChoiceArticle

Machine Learning Electron Density Prediction Using Weighted Smooth Overlap of Atomic Positions

by Siddarth K. Achar, Leonardo Bernasconi and J. Karl Johnson

Nanomaterials 2023, 13(12), 1853; https://doi.org/10.3390/nano13121853 - 13 Jun 2023

Cited by 4 | Viewed by 3987

Abstract

Having access to accurate electron densities in chemical systems, especially for dynamical systems involving chemical reactions, ion transport, and other charge transfer processes, is crucial for numerous applications in materials chemistry. Traditional methods for computationally predicting electron density data for such systems include [...] Read more.

Having access to accurate electron densities in chemical systems, especially for dynamical systems involving chemical reactions, ion transport, and other charge transfer processes, is crucial for numerous applications in materials chemistry. Traditional methods for computationally predicting electron density data for such systems include quantum mechanical (QM) techniques, such as density functional theory. However, poor scaling of these QM methods restricts their use to relatively small system sizes and short dynamic time scales. To overcome this limitation, we have developed a deep neural network machine learning formalism, which we call deep charge density prediction (DeepCDP), for predicting charge densities by only using atomic positions for molecules and condensed phase (periodic) systems. Our method uses the weighted smooth overlap of atomic positions to fingerprint environments on a grid-point basis and map it to electron density data generated from QM simulations. We trained models for bulk systems of copper, LiF, and silicon; for a molecular system, water; and for two-dimensional charged and uncharged systems, hydroxyl-functionalized graphane, with and without an added proton. We showed that DeepCDP achieves prediction

R^{2}

values greater than 0.99 and mean squared error values on the order of

10^{- 5}

e^{2}

Å

^{- 6}

for most systems. DeepCDP scales linearly with system size, is highly parallelizable, and is capable of accurately predicting the excess charge in protonated hydroxyl-functionalized graphane. We demonstrate how DeepCDP can be used to accurately track the location of charges (protons) by computing electron densities at a few selected grid points in the materials, thus significantly reducing the computational cost. We also show that our models can be transferable, allowing prediction of electron densities for systems on which it has not been trained but that contain a subset of atomic species on which it has been trained. Our approach can be used to develop models that span different chemical systems and train them for the study of large-scale charge transport and chemical reactions. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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10 pages, 2581 KiB

Open AccessArticle

Multicolor Tunable Electrochromic Materials Based on the Burstein–Moss Effect

by Xia Zhou, Enhui Huang, Rui Zhang, Hui Xiang, Wenying Zhong and Bo Xu

Nanomaterials 2023, 13(10), 1580; https://doi.org/10.3390/nano13101580 - 9 May 2023

Cited by 6 | Viewed by 2002

Abstract

Inorganic electrochromic (EC) materials, which can reversibly switch their optical properties by current or potential, are at the forefront of commercialization of displays and smart windows. However, most inorganic EC materials have challenges in achieving multicolor tunability. Here, we propose that the Burstein–Moss [...] Read more.

Inorganic electrochromic (EC) materials, which can reversibly switch their optical properties by current or potential, are at the forefront of commercialization of displays and smart windows. However, most inorganic EC materials have challenges in achieving multicolor tunability. Here, we propose that the Burstein–Moss (BM) effect, which could widen the optical gap by carrier density, could be a potential mechanism to realize the multicolor tunable EC phenomenon. Degenerated semiconductors with suitable fundament band gaps and effective carrier masses could be potential candidates for multicolor tunable EC materials based on the BM effect. We select bulk Y₂CF₂ as an example to illustrate multicolor tunability based on the BM effect. In addition to multicolor tunability, the BM effect also could endow EC devices with the ability to selectively modulate the absorption for near infrared and visible light, but with a simpler device structure. Thus, we believe that this mechanism could be applied to design novel EC smart windows with unprecedented functions. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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13 pages, 6461 KiB

Open AccessArticle

Lattice Thermal Conductivity of Monolayer InSe Calculated by Machine Learning Potential

by Jinsen Han, Qiyu Zeng, Ke Chen, Xiaoxiang Yu and Jiayu Dai

Nanomaterials 2023, 13(9), 1576; https://doi.org/10.3390/nano13091576 - 8 May 2023

Cited by 8 | Viewed by 2476

Abstract

The two-dimensional post-transition-metal chalcogenides, particularly indium selenide (InSe), exhibit salient carrier transport properties and evince extensive interest for broad applications. A comprehensive understanding of thermal transport is indispensable for thermal management. However, theoretical predictions on thermal transport in the InSe system are found [...] Read more.

The two-dimensional post-transition-metal chalcogenides, particularly indium selenide (InSe), exhibit salient carrier transport properties and evince extensive interest for broad applications. A comprehensive understanding of thermal transport is indispensable for thermal management. However, theoretical predictions on thermal transport in the InSe system are found in disagreement with experimental measurements. In this work, we utilize both the Green–Kubo approach with deep potential (GK-DP), together with the phonon Boltzmann transport equation with density functional theory (BTE-DFT) to investigate the thermal conductivity (

κ

) of InSe monolayer. The

κ

calculated by GK-DP is 9.52 W/mK at 300 K, which is in good agreement with the experimental value, while the

κ

predicted by BTE-DFT is 13.08 W/mK. After analyzing the scattering phase space and cumulative

κ

by mode-decomposed method, we found that, due to the large energy gap between lower and upper optical branches, the exclusion of four-phonon scattering in BTE-DFT underestimates the scattering phase space of lower optical branches due to large group velocities, and thus would overestimate their contribution to

κ

. The temperature dependence of

κ

calculated by GK-DP also demonstrates the effect of higher-order phonon scattering, especially at high temperatures. Our results emphasize the significant role of four-phonon scattering in InSe monolayer, suggesting that combining molecular dynamics with machine learning potential is an accurate and efficient approach to predict thermal transport. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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13 pages, 11345 KiB

Open AccessEditor’s ChoiceArticle

First-Principles Calculation of MoO₂ and MoO₃ Electronic and Optical Properties Compared with Experimental Data

by Eleonora Pavoni, Mircea Gabriel Modreanu, Elaheh Mohebbi, Davide Mencarelli, Pierluigi Stipa, Emiliano Laudadio and Luca Pierantoni

Nanomaterials 2023, 13(8), 1319; https://doi.org/10.3390/nano13081319 - 9 Apr 2023

Cited by 8 | Viewed by 4064

Abstract

MoO₃ and MoO₂ systems have attracted particular attention for many widespread applications thanks to their electronic and optical peculiarities; from the crystallographic point of view, MoO₃ adopts a thermodynamically stable orthorhombic phase (α-MoO₃) belonging to the space group [...] Read more.

MoO₃ and MoO₂ systems have attracted particular attention for many widespread applications thanks to their electronic and optical peculiarities; from the crystallographic point of view, MoO₃ adopts a thermodynamically stable orthorhombic phase (α-MoO₃) belonging to the space group Pbmn, while MoO₂ assumes a monoclinic arrangement characterized by space group P2₁/c. In the present paper, we investigated the electronic and optical properties of both MoO₃ and MoO₂ by using Density Functional Theory calculations, in particular, the Meta Generalized Gradient Approximation (MGGA) SCAN functional together with the PseudoDojo pseudopotential, which were used for the first time to obtain a deeper insight into the nature of different Mo–O bonds in these materials. The calculated density of states, the band gap, and the band structure were confirmed and validated by comparison with already available experimental results, while the optical properties were validated by recording optical spectra. Furthermore, the calculated band-gap energy value for the orthorhombic MoO₃ showed the best match to the experimental value reported in the literature. All these findings suggest that the newly proposed theoretical techniques reproduce the experimental evidence of both MoO₂ and MoO₃ systems with high accuracy. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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18 pages, 3259 KiB

Open AccessArticle

Redox Chemistry of the Subphases of α-CsPbI₂Br and β-CsPbI₂Br: Theory Reveals New Potential for Photostability

by Lavrenty Gennady Gutsev, Sean Nations, Bala Ramu Ramachandran, Gennady Lavrenty Gutsev, Shengnian Wang, Sergei Aldoshin and Yuhua Duan

Nanomaterials 2023, 13(2), 276; https://doi.org/10.3390/nano13020276 - 9 Jan 2023

Cited by 4 | Viewed by 2075

Abstract

The logic in the design of a halide-mixed APb(I_1−xBr_x)₃ perovskite is quite straightforward: to combine the superior photovoltaic qualities of iodine-based perovskites with the increased stability of bromine-based perovskites. However, even small amounts of Br doped into the [...] Read more.

The logic in the design of a halide-mixed APb(I_1−xBr_x)₃ perovskite is quite straightforward: to combine the superior photovoltaic qualities of iodine-based perovskites with the increased stability of bromine-based perovskites. However, even small amounts of Br doped into the iodine-based materials leads to some instability. In the present report, using first-principles computations, we analyzed a wide variety of α-CsPbI₂Br and β-CsPbI₂Br phases, compared their mixing enthalpies, explored their oxidative properties, and calculated their hole-coupled and hole-free charged Frenkel defect (CFD) formations by considering all possible channels of oxidation. Nanoinclusions of bromine-rich phases in α-CsPbI₂Br were shown to destabilize the material by inducing lattice strain, making it more susceptible to oxidation. The uniformly mixed phase of α-CsPbI₂Br was shown to be highly susceptible towards a phase transformation into β-CsPbI₂Br when halide interstitial or halide vacancy defects were introduced into the lattice. The rotation of PbI₄Br₂ octahedra in α-CsPbI₂Br allows it either to transform into a highly unstable apical β-CsPbI₂Br, which may phase-segregate and is susceptible to CFD, or to phase-transform into equatorial β-CsPbI₂Br, which is resilient against the deleterious effects of hole oxidation (energies of oxidation >0 eV) and demixing (energy of mixing <0 eV). Thus, the selective preparation of equatorial β-CsPbI₂Br offers an opportunity to obtain a mixed perovskite material with enhanced photostability and an intermediate bandgap between its constituent perovskites. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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12 pages, 2468 KiB

Open AccessArticle

The Effect of Y Doping on Monoclinic, Orthorhombic, and Cubic Polymorphs of HfO₂: A First Principles Study

by Eleonora Pavoni, Elaheh Mohebbi, Davide Mencarelli, Pierluigi Stipa, Emiliano Laudadio and Luca Pierantoni

Nanomaterials 2022, 12(23), 4324; https://doi.org/10.3390/nano12234324 - 5 Dec 2022

Cited by 13 | Viewed by 2421

Abstract

HfO₂ can assume different crystalline structures, such as monoclinic, orthorhombic, and cubic polymorphs, each one characterized by unical properties. The peculiarities of this material are also strongly related to the presence of doping elements in the unit cell. Thus, the present paper [...] Read more.

HfO₂ can assume different crystalline structures, such as monoclinic, orthorhombic, and cubic polymorphs, each one characterized by unical properties. The peculiarities of this material are also strongly related to the presence of doping elements in the unit cell. Thus, the present paper has the main purpose of studying and comparing twelve different systems characterized by diverse polymorphs and doping percentages. In particular, three different crystalline structures were considered: the monoclinic P2₁/c, the orthorhombic Pca2₁, and the cubic Fm $\bar{3}$ m phases of HfO₂. Each one has been studied by using Y as a doping agent with three different contents: 0% Y:HfO₂, 8% Y:HfO₂, 12% Y:HfO₂, and 16% Y:HfO₂. For all the systems, density functional theory (DFT) methods based on PBE/GGA, and on the HSE hybrid functionals were used to optimize the geometry as well as to study their optical properties. Depending on the polymorphs, Y affects the formation energy in different ways and causes changes in the optical properties. When the percentage of Y did not exceed 12%, a stabilization of the cubic phase fraction and an increase of the dielectric constant was observed. Additionally, the calculated optical bandgap energies and the refractive index are examined to provide an overview of the systems and are compared with experimental data. The bandgaps obtained are in perfect agreement with the experimental values and show a slight increase as the doping percentage grows, while only minor differences are found between the three polymorphs in terms of both refractive index and optical band gap. The adopted first principles study generates a reasonable prediction of the physical-chemical properties of all the systems, thus identifying the effects of doping phenomena. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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42 pages, 17969 KiB

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Current State of Computational Modeling of Nanohelicenes

by Vitaly V. Porsev and Robert A. Evarestov

Nanomaterials 2023, 13(16), 2295; https://doi.org/10.3390/nano13162295 - 9 Aug 2023

Cited by 3 | Viewed by 1327

Abstract

This review considers the works that focus on various aspects of the theoretical description of nanohelicenes (other equivalent names are graphene spirals, graphene helicoid, helical graphene nanoribbon, or helical graphene)—a promising class of one-dimensional nanostructures. The intrinsic helical topology and continuous π-system lead [...] Read more.

This review considers the works that focus on various aspects of the theoretical description of nanohelicenes (other equivalent names are graphene spirals, graphene helicoid, helical graphene nanoribbon, or helical graphene)—a promising class of one-dimensional nanostructures. The intrinsic helical topology and continuous π-system lead to the manifestation of unique optical, electronic, and magnetic properties that are also highly dependent on axial and torsion strains. In this paper, it was shown that the properties of nanohelicenes are mainly associated with the peripheral modification of the nanohelicene ribbon. We have proposed a nomenclature that enables the classification of all nanohelicenes as modifications of some prototype classes. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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28 pages, 7252 KiB

Open AccessReview

Advances in Metal–Organic Frameworks for the Removal of Chemical Warfare Agents: Insights into Hydrolysis and Oxidation Reaction Mechanisms

by Madeleine C. Oliver and Liangliang Huang

Nanomaterials 2023, 13(15), 2178; https://doi.org/10.3390/nano13152178 - 26 Jul 2023

Cited by 7 | Viewed by 2357

Abstract

The destruction of chemical warfare agents (CWAs) is a crucial area of research due to the ongoing evolution of toxic chemicals. Metal–organic frameworks (MOFs), a class of porous crystalline solids, have emerged as promising materials for this purpose. Their remarkable porosity and large [...] Read more.

The destruction of chemical warfare agents (CWAs) is a crucial area of research due to the ongoing evolution of toxic chemicals. Metal–organic frameworks (MOFs), a class of porous crystalline solids, have emerged as promising materials for this purpose. Their remarkable porosity and large surface areas enable superior adsorption, reactivity, and catalytic abilities, making them ideal for capturing and decomposing target species. Moreover, the tunable networks of MOFs allow customization of their chemical functionalities, making them practicable in personal protective equipment and adjustable to dynamic environments. This review paper focuses on experimental and computational studies investigating the removal of CWAs by MOFs, specifically emphasizing the removal of nerve agents (GB, GD, and VX) via hydrolysis and sulfur mustard (HD) via selective photooxidation. Among the different MOFs, zirconium-based MOFs exhibit extraordinary structural stability and reusability, rendering them the most promising materials for the hydrolytic and photooxidative degradation of CWAs. Accordingly, this work primarily concentrates on exploring the intrinsic catalytic reaction mechanisms in Zr-MOFs through first-principles approximations, as well as the design of efficient degradation strategies in the aqueous and solid phases through the establishment of Zr-MOF structure–property relationships. Recent progress in the tuning and functionalization of MOFs is also examined, aiming to enhance practical CWA removal under realistic battlefield conditions. By providing a comprehensive overview of experimental findings and computational insights, this review paper contributes to the advancement of MOF-based strategies for the destruction of CWAs and highlights the potential of these materials to address the challenges associated with chemical warfare. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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12 pages, 403 KiB

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Slater–Pauling Behavior in Half-Metallic Heusler Compounds

by Iosif Galanakis

Nanomaterials 2023, 13(13), 2010; https://doi.org/10.3390/nano13132010 - 5 Jul 2023

Cited by 15 | Viewed by 3042

Abstract

Heusler materials have become very popular over the last two decades due to the half-metallic properties of a large number of Heusler compounds. The latter are magnets that present a metallic behavior for the spin-up and a semiconducting behavior for the spin-down electronic [...] Read more.

Heusler materials have become very popular over the last two decades due to the half-metallic properties of a large number of Heusler compounds. The latter are magnets that present a metallic behavior for the spin-up and a semiconducting behavior for the spin-down electronic band structure leading to a variety of spintronic applications, and Slater–Pauling rules have played a major role in the development of this research field. These rules have been derived using ab initio electronic structure calculations and directly connecting the electronic properties (existence of spin-down energy gap) to the magnetic properties (total spin magnetic moment). Their exact formulation depends on the half-metallic family under study and can be derived if the hybridization of the orbitals at various sites is taken into account. In this review, the origin and formulation of the Slater–Pauling rules for various families of Heusler compounds, derived during these two last decades, is presented. Full article

(This article belongs to the Special Issue First-Principle Calculation Study of Nanomaterials)

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