HSE06 Level Research Articles

Electronic structure and theoretical exfoliation of non-van der Waals carbonates into low-dimensional materials: A case of Y2(CO3)3

The unique properties of two-dimensional (2D) materials make them highly versatile for a wide range of applications. Recently, low-dimensional structures obtained from bulk non-van der Waals materials have received particular interest. Yttrium carbonate is an example of such materials which hold the potential for creating 2D structures, however, its fundamental properties have been investigated only rarely. In this work, we demonstrate the possibility of obtaining 2D yttrium carbonate with the tengerite-(Y) structure. The electronic and optical properties of both bulk and two-dimensional Y2(CO3)3·2H2O are investigated using the PBE and HSE06 functionals. While the bulk material is predicted with a bandgap of 7.06 eV at the HSE06 level, the 2D Y2(CO3)3·2H2O material possesses a bandgap of, untypically, 0.4 eV narrower than the bulk material due to surface effects and different stoichiometry. The optical properties reveal that both the bulk and 2D forms are transparent in the visible and near-UV regions positioning them as promising candidates for various optical applications including doping-induced luminescent devices.

Stability, electronic and magnetic properties of boronphosphide (BP) graphenylene induced by interstitial atomic doping

In the context of low-dimensional materials, incorporating foreign atoms through doping processes has the potential to modulate the properties of host materials, which is favorable for diverse functional applications. In this study, we introduce a series of six distinct B6P6X ternary graphenylene monolayers. The B6P6X is designed through interstitial X = Cl, Br, I, O, S, and Te atomic doping of pure BP graphenylene. Through spin-polarized density functional theory (DFT), we comprehensively investigate the stability, electronic, and magnetic properties of B6P6X monolayers. We demonstrate that B6P6X monolayers are mechanically, dynamically and thermally stable with ferromagnetic ground state properties. We show that the metallic features of B6P6X (X = Cl, Br, I, O, S) and half-metallic property of B6P6Te monolayers at the PBE level can be further modulated when subjected to the HSE06 level. It is revealed that the B6P6X (X = O, S) monolayers exhibit a sizeable magnetic moment and a large magnetic anisotropy energy (MAE) value with an easy out-of-plane magnetization axis. We also found an out-of-plane MAE magnetization axis for B6P6X (X = Br, I) monolayers and an in-plane easy magnetization axis for B6P6X (X = Cl, Te) monolayers. Further investigation show that the B6P6S monolayer exhibit above room-temperature TC up to 565 K. The estimated Berezinskii–Kosterlitz–Thouless transition (BKT) temperature value of B6P6Te monolayer is 254 K. Our findings show that the B6P6X monolayers, particularly doped with chalcogens are potential candidates for nanoscale electronics and spintronics applications.

Large valley splitting induced by spin-orbit coupling effects in monolayer Hf3N2O2

Valleytronics is an emerging field of electronics that aims to utilize valley degrees of freedom in materials for information processing and storage. Nowadays, the valley splitting of 2D materials is not particularly large, therefore, the search for large valley splitting materials is very important for the development of valleytronics. This work theoretically predicts that MXene Hf3N2O2 is a 2D material with large valley splitting. It is an indirect bandgap semiconductor with a bandgap of 0.32 eV at the PBE level and increases to 0.55 eV at the HSE06 level. Since Hf3N2O2 breaks the symmetry of spatial inversion, when we consider spin–orbit coupling (SOC), there is a valley splitting at K/K′ of the valence band with a valley splitting value of 98.76 meV. The valley splitting value slightly decreases to 88.96 meV at the HSE06 level. In addition, The phonon spectrum and elastic constants indicate that it is both dynamically and mechanically stable. According to the maximum localization of the Wannier function, it is obtained that the Berry curvature is not zero at K/K′. When a biaxial strain is applied, Hf3N2O2 transitions from metal to semiconductor. With increasing biaxial strain, the valley splitting value increased from 70.13 meV to 109.11 meV. Our research shows that Hf3N2O2 is a promising material for valleytronics.

ZnS and CdS counterparts of biphenylene lattice: A density functional theory prediction

This study presents four novel inorganic structures based on the biphenylene network (BPN): planar BPN-ZnS (p-BPN-ZnS) and BPN-CdS (p-BPN-CdS) and buckled BPN-ZnS (b-BPN-ZnS) and BPN-CdS (b-BPN-CdS). Cohesive energy analyses reveal that structural buckling enhances stability, and a perturbation is necessary to obtain planar lattices. Phonon dispersion and ab initio molecular dynamics (AIMD) simulations demonstrated the dynamical and thermal stabilities. ZnS-based structures exhibited more pronounced charge accumulation and depletion than CdS. All evaluated structures are ultra-wideband gap semiconductors, with band gap energy values of 4.33, 5.34, 3.59, and 4.30 eV (at HSE06 level) for p-BPN-ZnS, b-BPN-ZnS, p-BPN-CdS, and b-BPN-CdS, respectively. p-BPN-ZnS demonstrated the highest Young modulus (Yx/Yy = 25.295/34.874 N/m), followed by p-BPN-CdS (Yx/Yy = 15.286/21.339 N/m). On the other hand, b-BPN-ZnS and b-BPN-CdS exhibit lower Young Modulus, Yx/Yy = 4.135/14.709 and 11.842/8.218 N/m, respectively. Notably, b-BPN-ZnS displayed a particular characteristic, a negative Poisson ratio (νx/νy = -0.008/-0.030), being an auxetic material. This report is expected to stimulate both theoretical and experimental researchers in the prediction and development of new inorganic materials based on the biphenylene network.

Single-layer and bilayer In2SeO2: Direct bandgap and reduced exciton binding from first-principles calculation

Two-dimensional semiconductors having direct bandgaps and weak exciton binding are necessary for highly integrated optoelectronic devices. Herein, single-layer (SL) and bilayer (AA and AB) In2SeO2 are proposed for the first time and studied using first-principles calculations. Both SL and bilayer In2SeO2 are of experimental feasibility for good stability. SL and bilayer AB In2SeO2 show moderate direct bandgaps at the HSE06 level. Their abundant visible-light absorption and weak exciton binding promise the successful generation of separated carriers. The high electron mobility of SL (∼3000 cm2·V−1·s−1) and bilayer AB (∼2600 cm2·V−1·s−1) suggests the possible application in electronics. The effective separation of electrons and holes is further confirmed by the huge discrepancy in carrier mobility and long-lived charge carriers. Summarily, our calculations support that In2SeO2 is a promising candidate in ultrathin optoelectronic devices.

Deep insight into structural and optoelectronic properties of mixed anion perovskites

Abstract Here we present the optoelectronic properties of pure inorganic lead-free halide perovskites in the form of Cs2AgBiX 6 (X = Br, Cl, F, I) using the density functional theory calculations on cubic phase (Fm 3 ̅ m) and tetragonal phase (I4/m). First, all the structures of the two phases were optimized at the PBE level. Structural, electronic, optical properties, phonon, and thermal properties of Cs2AgBiX 6 in cubic (Fm 3 ̅ m) and tetragonal phases (I4/m) were obtained using the VASP code. Tetragonal phases of all compounds of the form Cs2AgBiX 6, except Cs2AgBiBr6, are reported here for the very first time. Among all the Cs2AgBiX 6 (X = F, Cl, Br, I) structures, the cubic phase of Cs2AgBiBr6 was seen to have the highest absorption coefficient along with prominent electronic features that are favorable for optoelectronic applications. Thus, the cubic phase of Cs2AgBiBr6 was selected as the host lattice and bromine atoms were partly replaced with chlorine and iodine atoms. Electronic and optical properties of these mixed halide compounds of Cs2AgBiBr6−xFx, Cs2AgBiBr6−xClx, and Cs2AgBiBr6−xIx where x = 1, 2, 3, 4, 5 are investigated with hybrid functional HSE06 level. The electronic structure revealed that these mixed compounds exhibited indirect band gap nature regardless of the halide substitution (different x concentration) and the band gap of Cs2AgBiBr6 could be varied with the substitutions of fluorine, chlorine, and iodine atoms. Our in-depth analysis shows that Cs2AgBiBr6 and their mixed halides have the potential to become active double perovskite materials for photovoltaic applications and as photocatalysts for water splitting.

Insights into the DHQ-BN: mechanical, electronic, and optical properties

Computational materials research is vital in improving our understanding of various class of materials and their properties, contributing valuable information that helps predict innovative structures and complement empirical investigations. In this context, DHQ-graphene recently emerged as a stable two-dimensional carbon allotrope composed of decagonal, hexagonal, and quadrilateral carbon rings. Here, we employ density functional theory calculations to investigate the mechanical, electronic, and optical features of its boron nitride counterpart (DHQ-BN). Our findings reveal an insulating band gap of 5.11 eV at the HSE06 level and good structural stability supported by phonon calculations and ab initio molecular dynamics simulations. Moreover, DHQ-BN exhibits strong ultraviolet (UV) activity, suggesting its potential as a highly efficient UV light absorber. Its mechanical properties, including Young’s modulus (230 GPa) and Poisson’s ratio (0.7), provide insight into its mechanical resilience and structural stability.

First-principles calculations of inorganic metallocene nanowires.

Inspired by the recently synthesized inorganic metallocene derivatives Fe(P4)22-, we have identified four stable inorganic metallocene nanowires, MP4 (M = Sc, Ti, Cr and Fe) in configurations of either regular quadrangular prism (Q-type) or anticube (A-type), and further investigated their magnetic and electronic characteristics utilizing the first-principles calculation. It shows that CrP4 is a ferromagnetic metal, while other nanowires are semiconducting antiferromagnets with bandgaps of 0.44, 1.88, and 2.29 eV within the HSE06 level. It also shows that both ScP4 and TiP4 can be stabilized in the Q-type and A-type, corresponding to the antiferromagnetic and ferromagnetic ground states, respectively, indicating a configuration-dependent magnetism. The thermodynamic and lattice stabilities are confirmed by the ab initio molecular dynamics and phonon spectra. This study has unmasked the structural and physical properties of novel inorganic metallocene nanowires, and revealed their potential application in spintronics.

A new highly stable multifunctional two-dimensional Si2BN monolayer quantum material with a direct bandgap predicted by density functional theory.

In this work, we present a novel two-dimensional (2D) Si2BN structure (2D δ-Si2BN) predicted using density functional theory (DFT). The proposed structure exhibits a unique double quasi-planar layer interconnected by covalent bonds, demonstrating lower energy compared to the previously reported planar Si2BN nanosheet. Our calculations, conducted at the HSE06 level of theory, reveal its semiconductor nature with a direct band gap of 1.24 eV at the gamma point. The 2D material exhibits exceptional light absorption in the visible region, prompting an exploration of its potential in photovoltaic applications. Remarkably, our findings indicate a maximum theoretical efficiency of 27.6%, underscoring its promise for renewable energy technologies. Furthermore, employing modern polarization theory, we unveil the ferroelectric properties of the Si2BN monolayer. Notably, a large out-of-plane polarization is observed. It was found that the unstrained 2D δ-Si2BN monolayer demonstrates an impressive out-of-plane spontaneous electric polarization of 28.98 × 10-10 C m-1, a value six times greater than previously referenced Janus materials. This remarkable enhancement in ferroelectric capabilities positions the Si2BN monolayer as a promising candidate for applications in next generation novel information storage, nano-electronic, and optoelectronic devices. These findings not only contribute to the understanding of the structural and electronic properties of the 2D δ-Si2BN monolayer but also highlight its potential for various technological applications, marking a significant advancement in the field of nanomaterials.

Rational design of 2D Janus P3m1 M2N3 (M = Cu, Zr, and Hf) and their surface-functionalized derivatives: ferromagnetic, piezoelectric, and photocatalytic properties.

In this study, first-principles calculations were employed to rationally design two-dimensional (2D) Janus transition metal nitrides of P3m1 M2N3 phases, where M is a d-block element (Sc-Zn, Y-Cd, Hf-Hg). Among the 29 examined 2D M2N3, three 2D phases, namely P3m1 Cu2N3, Zr2N3, and Hf2N3, exhibit excellent thermodynamic, dynamic, mechanical, and thermal stabilities. These novel Janus 2D materials exhibit ferromagnetic metallic and half-metallic behavior. The related 2D Janus surface-functionalized derivatives, Cu2N3H, Cu2N3F, Cu2N3Cl, Zr2N3H, Hf2N3H, and Hf2N3F, are all dynamically stable. The 2D Janus P3m1 phases of Zr2N3H, Hf2N3H, and Hf2N3F, all with M in the +IV oxidation state, act as semiconductors in the visible region, with energy band gaps of 2.26-2.70 eV at the HSE06 level of theory. On the other hand, the 2D Janus P3m1 Cu2N3X phases (where X = H, F, and Cl) are ferromagnetic half-metals. Additionally, it has been unveiled that there are high hole mobilities (∼6 × 103 cm2 V-1 s-1) derived from the moderate deformation potential and effective mass in the 2D Janus P3m1 Zr2N3H, Hf2N3H, and Hf2N3F phases. Uniaxial strain engineering has demonstrated the outstanding in-plane piezoelectric properties of 2D Janus P3m1 Zr2N3H, Hf2N3H, and Hf2N3F with high d11 values (∼99.91 pm V-1). Furthermore, the desirable band-edge alignments and high anisotropic carrier mobilities of 2D Janus P3m1 Zr2N3H, Hf2N3H, and Hf2N3F phases indicate their potential as visible light-driven photocatalysts for water splitting reactions on different facets. These properties render 2D Janus P3m1 Zr2N3H, Hf2N3H, and Hf2N3F phases promising for use in optoelectronics, piezoelectric sensing, and photocatalysis applications.

Predicting [formula omitted]-BN: Computational insights into its mechanical, electronic, and optical characteristics

Computational materials are pivotal in understanding various material classes and their properties. They offer valuable insights for predicting novel structures and complementing experimental approaches. In this context, PSI (Ψ)-graphene has recently emerged as a stable two-dimensional carbon allotrope composed of 5-6-7 carbon rings. Using Density Functional Theory (DFT) calculations, we explored its boron nitride counterpart’s mechanical, electronic, and optical characteristics, Ψ-BN. Our findings reveal that Ψ-BN possesses a band gap of 4.59 eV, as determined at the HSE06 level. Phonon calculations and ab initio molecular dynamics simulations demonstrate its structural and dynamic stability. Ψ-BN exhibits a low formation energy of −7.48 eV. Moreover, we observe strong ultraviolet (UV) activity in Ψ-BN, implying its potential as an efficient UV collector. We have also determined its critical mechanical properties, including elastic stiffness constants, Young’s modulus (ranging from 250 to 300 GPa), and a Poisson ratio of 0.7, collectively providing valuable insights into its mechanical behavior.

A DFT study on the mechanical, electronic, thermodynamic, and optical properties of GaN and AlN counterparts of biphenylene network

The biphenylene network (BPN) is notable in recent fabrication efforts to design new 2D materials. The stability of its boron nitride counterpart, BN-BPN, has been confirmed through numerical investigations. In this study, we conducted a density functional theory (DFT) analysis to examine the mechanical, electronic, thermodynamic, and optical properties of two other group-III counterparts of BPN: gallium nitride (BPN-GaN) and aluminum nitride (BPN-AlN). Our findings reveal that the band gap values for BPN-GaN and BPN-AlN are 2.3 eV and 3.2 eV, respectively, at the HSE06 level. Phonon- and energy-formation calculations and ab initio molecular dynamics (AIMD) simulations suggest that BPN-(Al,Ga)N has good structural and dynamic stabilities. BPN-GaN displayed negative phonon frequencies. However, results from AIMD simulations point to its structural integrity with no bond reconstructions at 1000 K. These materials exhibit noteworthy UV activity, promising prospects as UV collectors. The thermodynamic properties reveal that the heat capacity of both BPN-AlN and BPN-GaN increases with temperature, eventually reaching the Dulong–Petit limit at around 800 K. We also performed calculations to determine the electron- and hole-effective masses, charge carrier mobility, elastic stiffness constants, Young’s modulus, and Poisson ratio for both BPN-GaN and BPN-AlN, providing valuable insight into their electronic and mechanical properties.

Prediction of novel 2D metallic ferroelastic ferromagnet: Monoclinic CrTe2

By combining the USPEX evolutionary algorithm and density functional theory at the HSE06 level, we identified a new CrTe2 monolayer crystallizing in monoclinic phase with C2h symmetry, which is different from the well-known 1T-CrTe2 monolayer. The monoclinic phase is energetically favored over that in 1T phase, is thermodynamically, dynamically, and mechanically stable. The monoclinic phase is an intrinsically ferromagnetic metal with a relatively high Curie temperature of 215 K showing an out-of-plane easy axis with 25° off the z-axis. In particular, the predicted Curie temperature and out-of-plane ferromagnetic order are in agreement with the experimental evidence. In addition, a uniaxial strain can induce a ferroelastic switching together with the magnetic easy axis, resulting in a strong intrinsic magnetoelasticity. Our results open up a new possibility for the realization of novel two-dimensional ferromagnets and provide a platform for understanding the underlying physical mechanism.

The first-principles calculations of photocatalytic water splitting and photoelectric properties of two-dimensional MoxW1-xS2 and MoS2xSe2(1-x) alloys

The realization of ternary alloys by atomic substitution of two-dimensional (2D) transition metal dichalcogenides (TMDs) is an effective solution to modulate the optoelectronic properties of 2D materials. The MoxW1-xS2 and MoS2xSe2(1-x) (0 ≤ x ≤ 1) alloys with high stability are established and their electronic, optical and photocatalytic performances are systematically investigated based on the first-principles calculations. Our results indicate that the MoxW1-xS2 and MoS2xSe2(1-x) alloys remain direct bandgaps and optical adsorption has excellent ability to capture ultraviolet and visible light. Suitable bandgap at HSE06 level (>1.23 eV) and band edges satisfy the conditions of photocatalytic water splitting under acidic or neutral solutions. Biaxial strain can enhance the alloys direct bandgap ranges. The introductions of W and S in MoS2 and MoSe2 monolayers cause their intrinsic electronic properties to change. The bandgap values, effective masses and work functions as well as optical adsorption properties of the MoxW1-xS2 and MoS2xSe2(1-x) show different behaviors due to the d-d, p-p and d-p orbitals hybridization between Mo, W, S and Se atoms. The absorption coefficients of Mo0·5W0·5S2 and MoS1·5Se0.5 are significantly higher theirs pure binary TMDs. The work provides a valuable theoretical guidance of TMDs alloys application in 2D flexible photoelectric devices and photocatalytic water splitting.

Single-layer ZnGaInS4: Desirable bandgap and high carrier separation efficiency for optoelectronics

Two-dimensional optoelectronic materials with desirable bandgaps and high carrier separation efficiency are in urgent need. Herein, single-layer ZnGaInS4 is designed and thoroughly studied by first-principles calculations. Our calculations reveal the excellent stability of single-layer ZnGaInS4, and the small cleavage energy demonstrates the feasibility to exfoliate single-layer ZnGaInS4 from bulk counterparts. At the HSE06 level, single-layer ZnGaInS4 has a moderate bandgap of 2.05 eV, and its valence band maximum and conduction band minimum are spatially separated, thus impeding the electron-hole pair formation and enhancing the photoelectronic performance. In the visible region, single-layer ZnGaInS4 exhibits an optical absorption coefficient of ∼ 105 cm−1. Notably, single-layer ZnGaInS4 possesses high electron carrier mobility and low hole carrier mobility, further affirming the effective carrier separation. Another attractive characteristic is that single-layer ZnGaInS4 has anisotropic hole mobility. The desirable bandgap and high separation efficiency of generated carriers, together with abundant optical absorption, promise single-layer ZnGaInS4 is a hopeful candidate in atomic-thick optoelectronic devices.

Theoretical Study on Zigzag Boron Nitride Nanowires.

In this work, two kinds of BN-nanowires (BNnws): a-BNnw and d-BNnw, respectively composed of azo (N-N) and diboron (B-B) bonds, are proposed with the aid of the first-principles simulations. Their structural stabilities are carefully verified from the energetics, lattice dynamics, and thermodynamic perspectives. Similar to the other common boron nitride polymorph, the a-BNnw and d-BNnw are semiconductors with relatively wide band gaps of 3.256 and 4.631 eV at the HSE06 level, respectively. The corresponding projected DOS patterns point out that their band edges are composed of different atomic species, which can help with the separation of their excitons. The band gaps can be manipulated monotonically by axial strains within the elastic ranges. The major charge carriers are electron holes. Significantly, a-BNnw possesses very high carrier mobilities around 0.44×104 cm2 V-1 s-1 .

Large Magnetoresistance and Perfect Spin-Injection Efficiency in Two-Dimensional Strained VSi2N4 -Based Room-Temperature Magnetic-Tunnel-Junction Devices

Two-dimensional (2D) materials provide a promising platform for exploring spintronic devices. However, the low Curie temperature of most 2D magnetic materials limits their development and application. Based on density-functional theory and the nonequilibrium-Green's-function formalism, we present a systematic simulation study of room-temperature strained ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$-based magnetic tunnel junctions (MTJs), using a high-accuracy Heyd-Scuseria-Ernzerhof (HSE) functional. In contrast to Perdew-Burke-Ernzerhof results, a spin-conductance match is observed in $\mathrm{Ag}/{\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$-${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}/\mathrm{Ag}$ MTJs at the HSE06 level. Thus, a 1200% tunnel-magnetoresistance (TMR) ratio and a perfect spin-injection efficiency are theoretically predicted in $\mathrm{Ag}/{\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$-${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}/\mathrm{Ag}$ MTJs. Interestingly, the coexistence of a Weyl semimetal and a half-metal state is found in 1.965% tensile-biaxial-strained monolayer ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$. In addition, a slight compressive strain leads to a boost of the TMR ratio by 2 orders of magnitude, up to ${10}^{5}\mathrm{%}$ in strained ${\mathrm{VSi}}_{2}{\mathrm{N}}_{4}$-based MTJs. Other MTJs based on ${\mathrm{VSi}}_{2}{\mathrm{P}}_{4}$, ${\mathrm{VSi}}_{2}{\mathrm{As}}_{4}$, and ${\mathrm{Nb}\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ are investigated. Our results show that these spin-polarized magnetic silicide compounds, with Curie temperatures close to room temperature, are promising candidates for next-generation spintronic devices.

Two-dimensional MX2Y4 systems: ultrahigh carrier transport and excellent hydrogen evolution reaction performances.

Very recently, two-dimensional MoSi2N4 has been synthetized (Y.-L. Hong, Z. Liu, L. Wang, T. Zhou, W. Ma, C. Xu, S. Feng, L. Chen, M.-L. Chen and D.-M. Sun, Chemical vapor deposition of layered two-dimensional MoSi2N4 materials, Science, 2020, 369, 670-674.). In this work, we systematically explore the mechanical, electronic, and catalytic properties of the MX2Y4 (M = Cr, Hf, Mo, Ti, W, Zr; X = Si, Ge; Y = N, P, As) monolayers by first-principles calculations. These observed monolayers exhibit an isotropic Young's moduli of 165-514 N m-1 and a Poisson's ratio of 0.26-0.33. The calculated band structures indicate that their bandgaps are in the range of 0.49-2.05 eV at the HSE06 level. In particular, a high electron mobility of about 1.04 × 104 cm2 V-1 s-1 is observed in TiSi2N4 monolayers, which shows potential for high-speed electronic devices. MX2Y4 monolayers also reveal decent performances in the hydrogen evolution reaction. More importantly, the Gibbs free energy change of the TiSi2N4 (ZrSi2N4) monolayer is as small as 0.078 eV (-0.035 eV), even being comparable with that of Pt (-0.09 eV). This investigation suggests that the MoSi2N4 family monolayers have potential advanced applications such as photocatalytic, electrocatalytic, and photovoltaic devices.

Theoretical determination of superior high-temperature thermoelectricity in an n-type doped 2H-ZrI2 monolayer.

Two-dimensional materials with a competitive figure of merit zT are extremely desirable for the fabrication of thermoelectric modules. In the present work, we systematically evaluated the thermoelectricity of monolayer 2H-ZrI2 through first-principles calculations and semiclassical Boltzmann transport theory. Apart from its all-round structural stability and feasibility of experimental preparation, the semiconducting material with a moderate indirect bandgap of 1.07 eV at the HSE06 level exhibits an acceptable lattice thermal conductivity κL of 6.69 W m-1 K-1 at 900 K contributed dominantly by acoustic modes. The four-phonon scattering is found to exert a minor effect on the κL of the monolayer. Moreover, a quite large power factor of up to 147.89 mW m-1 K-2 can be achieved due to the conduction band valley degeneracy near the Fermi level. These transport coefficients eventually give rise to a significant optimal n-type zT value as high as 3.57 at 900 K at a certain experimentally achievable electron doping concentration. Our study demonstrates the potential application of monolayer 2H-ZrI2 in high-temperature thermoelectric devices.

Prediction of electronic and optical properties of monoclinic 1T’-phase OsSe2 monolayer using DFT principles

Following the discovery and characterization of transition metal dichalcogenides (TMDs) monolayers, which has created interest in last few years, it would seem natural to explore new possibilities of monolayers. Thus, using the density functional theory (DFT), we investigated the structural, electronic, vibrational and thermodynamic properties, and optical absorption of osmium selenide monolayer (monoclinic 1T’-phase OsSe 2 monolayer). We perform the calculations using the approaches based on the generalized gradient (GGA) and the local density (LDA) approximations for the optimized structure with the minimum energy, as well as we use the hybrid exchange–correlation functional HSE06 recommended in the literature for bandgap energy estimation. An indirect bandgap E g = 0 . 85 eV, E g = 0 . 95 eV and E g = 1 . 80 eV was obtained within the LDA-CAPZ, GGA-PBE and HSE06 level of calculation, respectively. The vibrational normal modes, infrared and Raman spectra were obtained and assigned in the frequency range of 0 − 400 c m − 1 together with the phonon dispersion relation. In addition, the optical absorption was shown to be sensitive to the plane of polarization of the incident light mainly in the range of UV radiation. The thermodynamic potentials and specific heat at constant volume were calculated and analyzed. These results indicated that the monoclinic 1T’-phase OsSe 2 structure could be potentially synthesized and bringing new potential technological applications.