Hybrid Functional Study Research Articles

Electronic Properties of Janus TMD WSSe/WX2 (X = S, Se) Heterostructure by External Strain: A Hybrid Functional Study

Electronic Properties of Janus TMD WSSe/WX₂ (X = S, Se) Heterostructure by External Strain: A Hybrid Functional Study

Assessment of Thermoelectric Properties of Bi2Se3: Insights from Hybrid Functional Studies, Strain Engineering, and Machine Learning Methodology

AbstractThermoelectric properties in topological insulator Bi2Se3 are explored with multifaceted strategies, i.e., hybrid functional with strain and artificial intelligence methodology. The assessment with the experimental band gap values recognizes the limitations of conventional functional and the effectiveness of screened hybrid functionals. A thorough investigation into the impact of biaxial and uniaxial strain on thermoelectric parameters uncovers distinctive behaviors in n‐type and p‐type Bi2Se3, providing insights into optimal strain conditions for improved performance. Furthermore, the studies on the role of topologically non‐trivial surface states (TNSS) in thermoelectric properties reveal that TNSS significantly dominate electronic transport. Dual scattering time approximation elucidates the segregation of thermoelectric transport contributions from bulk and surface states, highlighting the importance of controlling the relaxation time ratio for enhanced thermoelectric performance. Additionally, the prediction of thermoelectric properties using Random Forest and Neural Networks models showcase impressive agreement with density functional theory predictions across varying temperatures, offering a powerful tool for understanding complex temperature‐dependent trends in thermoelectric properties. In summary, this interdisciplinary study presents a unique approach to advancing the understanding and optimization of thermoelectric properties in Bi2Se3. It provides a comprehensive framework for tailoring material behavior for diverse thermoelectric applications.

The electronic structure, optical property and n-type conductivity for W-doped α-Ga2O3: hybrid functional study

Based on the hybrid functional method, the electronic structure, optical property and electron effective mass of α-Ga2O3, together with the properties for intrinsic and extrinsic defects incorporated into α-Ga2O3 are studied. Obtained results indicate the α-Ga2O3 possesses a wide band gap (5.31 eV), small electron effective mass (0.22 m0) and a high visible light transmittance. The nonstoichiometric α-Ga2O3 is not an excellent n-type semiconductor. To improve the n-type conductivity, the W-doped α-Ga2O3 is studied. We find that W Ga is a promising n-type defect due to its relatively small ionization energy ϵ(0/+) (0.30 eV). When the equilibrium fabrication method is selected, the WO2 is a promising dopant source. Using the equilibrium fabrication method, the defect complex (V O+ W Ga) would be formed, and the ionization energy ϵ(0/+) for defect complex (V O + W Ga) would decrease to 0.08 eV, which implies that a great number of free electrons could be induced in the samples. We expect that this work can promote the understanding of the n-type conductivity for α-Ga2O3 and provide significant insights for the development of a transparent n-type semiconductor.

Theoretical Perspective of Fe-Induced Ferromagnetism in Antimonene: A Hybrid Functional Study

Theoretical Perspective of Fe-Induced Ferromagnetism in Antimonene: A Hybrid Functional Study

The transparency and p-type defects for group IV atoms doped AlP: the hybrid functional study

Abstract The electronic structures and optical properties, together with the properties for intrinsic defects and group IV atoms doped AlP are studied by employing the hybrid functional method. Obtained results imply AlP is a promising transparent material, nonstoichiometric AlP is a potential n-type semiconductor. The transition energy level ε(0/-) for C, Si and Ge substituting P are 0.24, 0.33 and 0.48 eV above the valence band maximum (VBM), indicating C substituting P (written as CP) is a shallow p-type defect. With the thermal equilibrium fabricated method, the obvious self-compensation effect exists among the CP and the intrinsic defects, suggesting the non-equilibrium fabricated method, such as, the molecular beam epitaxy fabrication scheme, should be considered to fabricate the p-type CP defect.

Hybrid Functional Study on Electronic and Optical Properties of the Dopants in Anatase TiO2.

TiO2 was known as a golden heterogeneous photocatalyst due to its chemical stability, low cost, nontoxicity, and strong oxidizing power. However, anatase TiO2 predominantly absorbs the photon energy in the ultraviolet region (λ < 387.5 nm); therefore, to increase the utilization of sunlight, the approach of doping of metals and nonmetals into pure TiO2 is implemented. Here we incorporate the dopants of Zr, Si, V, W, Ge, Cr, Sn, Mo, and Pb into the TiO2 lattice and study the optoelectronic properties, including the formation energies and the electron charge distributions, using the Vienna ab initio Simulation Package (VASP) from the hybrid functional of Heyd, Scuseria, and Erhzerhof (HSE06). We observed that V-, Mo-, and Cr-doped systems introduce shallow impurity states within the band gap, and those states influence the shift of the absorbance spectra to visible light by enhancing the photocatalytic efficiency. W-doped anatase TiO2 structure reduces the band gap of the pure anatase TiO2 by 0.7 eV. Notably, this reduction occurs without the introduction of any impurity states between the band edges. Additionally, the absorption edge of the solar spectrum shifts toward lower photon energy from 3.5 to 3.1 eV. From Bader charge analysis, we observed that mainly the charge transfer occurred from the dopants and charge accumulation happened around nearby oxygen atoms. The ferromagnetism was observed in V-, Cr-, Mo-, and W-doped anatase TiO2 structures due to the charge imbalance of the spin-up and spin-down states.

Band engineering in monoclinic WO3 with C+H co-doping for optoelectronic applications: A hybrid functional study

Using the hybrid functional method, we systematically investigate the band engineering induced by C + H co-doping in monoclinic WO3, and the associated effect on the optoelectronic functionality as well. First, we find that C substitution for O in WO3 improves the optical absorption through narrowing the band gap by 11% and introducing a curved intermediate level within the band gap (which functions as a stepping stone to relay the excited valence electrons to the conduction band). Further H incorporation into C-doped WO3 stabilizes the C substitution via clustering with C in the form of C-H and H-C-H chains, which reduces the band gap to less than 2 eV and simultaneously drives the deep C-induced intermediate level to be shallow. Such dopant clustering and the induced band engineering remarkably promote the optical absorption and optoelectronic functionality of WO3. The positive influence of dopant clustering has been fully analysed and discussed, and the favorability for forming C-H and H-C-H clusters in WO3 has been well presented through the detailed thermodynamic and kinetic analyses. The outcome of this work is expected to offer insightful guidance to tuning the properties of WO3 materials towards optoelectronic applications.

Defect physics of intrinsic point defects in BiPO4 photocatalysts: a hybrid functional study.

In this work, the intrinsic point defect properties of bulk BiPO4 under different growth conditions are intensively investigated and explored using first-principles hybrid functional calculations. It is found that Bi vacancies and O vacancies are the primary native defects in BiPO4. Under O-poor conditions, BiPO4 acts as an intrinsic insulator because the O vacancy defects (donor) and the Bi vacancy defects (acceptor) compensate for each other. Under Bi-poor conditions, good p-type conductivity is observed in BiPO4, which affirms the observed p-type conductivity behavior in experiments. Bi vacancies in BiPO4 are very shallow, which make it an excellent acceptor and are mostly responsible for the p-type character. In addition, it is found that the primary Bi vacancy defects of BiPO4 hardly affect its electronic structure and optical absorption spectrum regardless of the charge states. In contrast, the neutral O vacancy defects in BiPO4 introduce an impurity energy level near the VBM and induce a new optical absorption peak at around 370 nm. Furthermore, the O vacancies should be favorable for enhancing the production and separation efficiencies of the photo-generated electrons and holes in BiPO4. While Bi vacancies easily provide p-type carriers, simultaneously, they could become the active sites for the photocatalytic reactions because of their dominant -3 charge state. Therefore, understanding the defect physics in BiPO4 photocatalysts is believed to be beneficial for more research in developing BiPO4 or BiPO4-based photocatalysts.

The transparency and p-type performance in B6P: The hybrid functional study

The transparency and p-type performance for B6P is investigated by the hybrid functional calculations. It is found that B6P is an indirect band gap semiconductor with a band gap of 3.23 eV. The hole effective mass along the T to Γ direction is only 0.35 m0, where m0 is the mass of the free electron. The B6P is a promising high transparent material due to its low absorption, low reflection, and high transmittance. For intrinsic B6P, BP (PB(B)) is the main defect under B-rich (P-rich) condition. The formation energy of the dominant defect is calculated. The thermodynamic simulation method is performed to quantitatively study the Fermi energy, hole concentration, and defect density. Our results show that quenching the intrinsic B6P from 1900 K to room temperature can increase the holes' density from 9.86 × 102 to 2.80 × 1013 cm−3. These results provide essential insight for B6P as a potential transparent p-type material.

Transparency and p-Type Conductivity of BeSe Doped with Group VA Atoms: A Hybrid Functional Study

Utilizing a hybrid functional method, the transparency and p-type conductivity of BeSe are investigated. Our studies confirm that N- and P-substituted Se (labeled as NSe and PSe) are promising p-type defects due to their smaller ionization energy. BeN2 and BeP2 are efficient dopant sources for their moderate formation energy. Based on the thermodynamic equilibrium fabrication method together with the rapidly quenching scheme, we find the hole density, induced by NSe (PSe) defects, can reach 4.44 × 1018 (3.83 × 1016) cm–3. A high density of holes, smaller hole effective mass (along the Γ-X and W-X directions, the hole effective masses are 0.466 and 0.759m0 (m0 is the electron’s static mass)), wide band gap, and weak plasmonic effect show that BeSe with NSe defects is an excellent transparent p-type semiconductor. These findings provide significant insight to explore a transparent p-type semiconductor.

Enhanced optoelectronic functionality of N + H codoped monoclinic WO3: A hybrid functional study

N + H co-doping in monoclinic WO 3 has been systematically investigated using the Heyd-Scuseria-Enrzerhof hybrid functional. Results show that N and H tend to stay nearest to each other to form a N H cluster, inducing a dispersive and occupied intermediate band within the band gap of WO 3 . The presence of this intermediate band makes the band gap narrowed by 24%, leading to a remarkable redshift of the optical absorption edge. Simultaneously, the high carrier mobility is beneficial for the electron excitation, also contributable to the enhancement in the photoabsorption of WO 3 . Especially, the N H bond length is very close to that in NH 3 , suggesting that it is likely to utilize NH 3 to dope WO 3 for improved optoelectronic performance. The thermodynamic and kinetic stabilities of the N H cluster in WO 3 have been addressed in details. This work has implications in optimizing the optoelectronic functionality of WO 3 -based materials for environmentally friendly applications.

Strain-driven modulation of the electronic, optical and thermoelectric properties of [formula omitted]-antimonene monolayer: A hybrid functional study

Electronic, optical, and thermoelectric properties of the β-antimonene (β-Sb) monolayer under the external biaxial strain effects are fully investigated through the first-principles calculations. The studied two-dimensional (2D) system is dynamically and structurally stable as examined via phonon spectrum and cohesive energy. At equilibrium, the β-Sb single layer exhibits an indirect band gap of 1.310 and 1.786 eV as predicted by the PBE and HSE06 functionals, respectively. Applying external strain may induce the indirect–direct gap transition and significant variation of the energy gap. The calculated optical spectra indicate the enhancement of the optical absorption in a wide energy range from infrared to ultraviolet as induced by the applied strain. In the visible and ultraviolet regime, the absorption coefficient can reach values as large as 82.700 (104/cm) and 91.458 (104/cm). Results suggest that the thermoelectric performance may be improved considerably by applying proper external strain with the figure of merit reaching a value of 0.665. Our work demonstrates that the external biaxial strains may be an effective method to make the β-Sb monolayer prospective 2D material for optoelectronic and thermoelectric applications.

S vacancy enhanced ferromagnetism in Mn-doped monolayer MoS2: A hybrid functional study

Abstract Electronic and magnetic properties of monolayer MoS2 with a Mn dopant and a native S vacancy (VS) has been systematically investigated using hybrid functional method, so as to predict and interpret the influence of VS on the magnetic properties of Mn-doped monolayer MoS2. Results show that the incorporation of VS in Mn-doped monolayer MoS2 causes excess electrons to localize at the VS site and the surrounding Mn and Mo atoms. This leads to the additional ferromagnetic contribution from the polarization of these localized electrons, effectively enhancing the ferromagnetism in Mn-doped monolayer MoS2. The importance of the clustering of VS and Mn substitution on the enhancement of ferromagnetism, and the stability of the Mn-VS cluster in monolayer MoS2 as well, have been discussed in detail. The present work is beneficial for deeply understanding the ferromagnetism in Mn-doped monolayer MoS2 and for promoting the applications of monolayer MoS2 in spintronics.

Hybrid Functional Study of H-Abstraction from Methane by Li-Doped, Pristine and Stepped MgO(100) and MgO(110) Surfaces

Hydrogen abstraction from CH4 to MgO is a key step in the oxidative coupling of methane. We investigated CH4 activation on Li-doped MgO, MgO(110), and stepped MgO with the density functional theory. Our calculations with hybrid functionals revealed that MgO(110) and stepped MgO are strong candidate as the active site.

Electronic and Transport Properties of Sn-Doped Sb2Te3: A Hybrid Functional Study

Electronic and Transport Properties of Sn-Doped Sb2Te3: A Hybrid Functional Study

S Vacancy Engineered Electronic and Optoelectronic Properties of Ni-Doped MoS2 Monolayer: A Hybrid Functional Study

The interaction between the substitutional Ni atom and the native S vacancy (VS) in the monolayer MoS2 has been systematically investigated using the Heyd–Scuseria–Ernzerhof hybrid functional method, aiming to elaborate how the VS engineers the electronic and optoelectronic properties of Ni-doped monolayer MoS2. The results show that VS tends to stay next to Ni substitution to form a cluster in the monolayer MoS2, which is found to be attributed to the strong attraction between them. With respect to Ni substitution alone, such a cluster induces more dispersive or delocalized intermediate bands within the band gap. These intermediate bands not only effectively act as stepping stones to relay valence electrons to the conduction band but also permit the multi-wavelength absorption of solar light, thus significantly enhancing the optical absorption of monolayer MoS2. Thermodynamic and kinetic investigations have been conducted to elaborate the favorability for the formation of the Ni-VS cluster in monolayer MoS2. The outcome of this work is beneficial for offering guidance for modulating the electronic and optoelectronic properties of monolayer MoS2 through defect engineering.

Asymmetric-dimer reconstruction and semiconducting properties of Mg2Si(100) surfaces: Prediction from meta-GGA and hybrid functional study

Mg2Si is an important semiconducting silicide material with promising applications in optoelectronics, thermoelectrics, and photovoltaics. Mg2Si(001)-(1 × 1) surfaces have been suggested to be metallic from density functional (DFT) studies performed within local density (LDA) and generalized gradient approximations (GGA). Here in this article, we revisit and further explore surface electronic structure, surface reconstruction and stability of Mg2Si(100) surfaces within DFT framework in combination with Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional as well as Tran-Blaha (TB09) meta-GGA functional for exchange-correlation. Our results suggest that reconstructed Mg2Si(100) surfaces are semiconducting which are incorrectly found as metallic in absence of reconstructions with higher surface periodicities and when computed within LDA (GGA) approximations. In particular, the Si-terminated Mg2Si(100) surface exhibits (2 × 1) reconstruction qualitatively similar to buckled asymmetric dimer type reconstruction of Si(100)-(2 × 1) surface. The band gap of Mg-terminated relaxed Mg2Si(100)-(1 × 1) and reconstructed Si-terminated Mg2Si(100)-(2 × 1) surfaces are found to be in the range ~ 0.3–0.5 eV. The Si-terminated reconstructed (2 × 1) surface is found to be lower in energy by ~0.21 J/m2 than the (1 × 1) relaxed surface. Further, localized surface states are formed in the band gap near valence band maximum (VBM) as well as at ~7 eV below the VBM depending on the surface termination. The surface localized gap states may be expected to have important implications for relaxations and thermodynamic energies of Mg2Si(100) surfaces.

Hybrid functional study of hydrogen passivation in carbon-oxygen related defect complexes in silicon

Density functional theory (DFT) with the Heyd-Scuseria-Ernzerhof hybrid functional was used to predict the structure, formation energy, stability and the charge state transition energy levels induced by carbon-oxygen related complexes as a result of hydrogen passivation in silicon. Our results show that, in the neutral charge state the hydrogen interstitial (Hi) interacts with Oi, Ci, CsOi, CiOi, and CsCi to form a stable OiHi, CiHi, CsOiHi, CiOiHi, and CsCiHi defect complexes. Predicted charge state transition levels showed reasonable agreement with the experiment. The charge state transition energy levels were found to shift to the conduction band as a result of hydrogen passivation.

Hybrid-Functional Study of Native Defects and W/Mo-Doped in Monoclinic-Bismuth Vanadate

Monoclinic scheelite (ms) BiVO4 is recognized as one of the most promising photocatalyst materials due to its band gap as well as band-edge positions. Several theoretical and experimental works hav ...

Native point defects and carbon clusters in 4H-SiC: A hybrid functional study

We report first-principles calculations that clarify the formation energies and charge transition levels of native point defects and carbon clusters in the 4H polytype of silicon carbide (4H-SiC) under a carbon-rich condition. We applied a hybrid functional that reproduces the experimental bandgap of SiC well and offers reliable defect properties. For point defects, we investigated single vacancies, antisites, and interstitials of Si and C on relevant sites. For carbon clusters, we systematically introduced two additional C atoms into the perfect 4H-SiC lattice with and without removing Si atoms and performed structural optimization to identify stable defect configurations. We found that neutral Si antisites are energetically favorable among Si-point defects in a wide range of the Fermi level position around the intrinsic regime, whereas negatively-charged Si vacancies and a positively-charged Si interstitial on a site surrounded by six Si and four C atoms become favorable under n- and p-type conditions, respectively. For C-point defects, neutral C antisites are favorable under intrinsic and n-type conditions, whereas positively-charged C vacancies become favorable under p-type conditions. We also found that a di-carbon antisite is more favorable than a C-split interstitial, which is the most stable form of single C interstitials.