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Present paper deals with the study of electronic and optical behaviour of a II 3 -V 2 group semiconductor compound Zn 3 N 2 and corresponding significant alterations, that are realised after H-adsorption on its (100) non-polar surface. Calculations are performed applying the linear combination of atomic orbitals method. The relative stability of H-adsorbed systems represents the adsorption to be energetically favourable, indicating possible applications in H-storage devices. A direct electronic band gap of 1.59 eV at gamma point is reported, which is further converted into conducting and again semiconducting for slab and adsorbed configurations, respectively. This tuning of the band gap is very important outcome that may emerge new possibilities in optoelectronic field. Further, favourable alterations are perceived in optical behaviour as well, allowing more absorption possibilities in the optimum range of solar radiations. Consequently, efficiencies are supposed to get enhanced. [Display omitted] ∙ Present study deals with the electronic and optical details of a controversial compound Zn 3 N 2 and the alterations that are realised after adsorbing atomic Hydrogen on its (100) non polar surface. ∙Major Vacillations in reported data are supposed to get settled down to some extent on the basis of these absolute theoretical outcomes. ∙Relative stability of the H-adsorbed systems represents the adsorption to be energetically favourable and in turn, indicating the potential applications in H-storage devices. ∙Tuning of the band gap is an important outcome that may emerge new possibilities in optoelectronic field. ∙Optical response of the material is also modified significantly, allowing more absorption possibilities in the optimum range of solar radiations. Consequently, efficiencies are supposed to get enhanced efficiently. [ABSTRACT FROM AUTHOR]

Novelty statement The CsMgX 3 (X=Cl and Br) compounds are investigated with respect to their electronic, thermoelectric and optical properties using FP-LAPW method with PBE-GGA and mBJ-GGA potentials. One of the novelties in the compounds noticed that they have excellent thermoelectric efficiency measured bypower factor (PF), henceforth figure of merit (ZT). We predict PF value 2.75 x1011 and 3.98 x1011W/K2ms for CsMgCl 3 and CsMgBr 3 , respectively at room temperature, which increases as temperature increases. Further, these materials display ZT values of 0.69 and 0.75 at room temperature, which approach to 0.97 and 0.99 at certain chemical potential for CsMgCl 3 and CsMgBr 3 , respectively. Consequently, promising materials for thermoelectric applications. [Display omitted] • Electronic band profile exhibit wide band gap of 6.35 and 4.26 eV, in CsMgCl 3 and CsMgBr 3 compounds, respectively. • Remarkable figure of merit, 0.69 and 0.75 at 300 K, which approaches to 0.97 and 0.99 at certain chemical potential for CsMgCl 3 and CsMgBr 3 , respectively. • Materials found suitable in UV region and can be employed as UV absorbers implanted in sensitive devices to protect from UV-rays. • Our work pronounces novel results and can be beneficial for the advancement in the thermoelectric applications as well. The electronic, thermoelectric and optical properties of cubic CsMgX 3 (X = Cl, Br) are performed using full potential augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ-GGA) approximation as exchange correlation potentials. The band profile of CsMgCl 3 and CsMgBr 3 using mBJ-GGA potentials exhibits indirect wide energy band gap of 6.35 and 4.26 eV, respectively. Further, thermoelectric properties are carried out as a function of temperature (100–1200 K) and chemical potential using BoltzTrap code. It has been found that thermoelectric efficiency increases with increasing temperature upto 1200 K. The figure of merit (ZT) values are calculated to 0.69 and 0.75 at room temperature for CsMgCl 3 and CsMgBr 3 , respectively. Furthermore, optical properties are computed in the energy spectrum (0–12 eV). These materials absorb light in ultra violet region and can be used as absorber of UV-rays. Also materials are suitable for thermoelectric power generator applications. [ABSTRACT FROM AUTHOR]

Structural, elastic, electronic and optical properties of zinc blende Cd 1- x - y Zn x Hg y Te quaternary alloys and their allied compounds are calculated with DFT based FP-LAPW approach. Structural and mechanical properties are computed with PBE-GGA potentials, while mBJ-GGA and GGA + U potentials are employed to compute electronic and optical properties. All the thermodynamically stable specimens show mechanical stability, elastic anisotropy, ductility, mixed type of bonding etc. Each alloy shows direct (Γ-Γ) band gap (E g) with E g m B J − G G A > E g G G A + U . Electrons play dominant role over holes in carrier transportation. Exclusive or collective effort of the Te-5p→Zn-5s, Cd-6s, Hg-7s electronic transitions contribute peaks in the ε 2 (ω) spectra of any specimen. Specimen with higher band gap possesses lower zero-frequency limits, but requires higher critical point energies in different optical spectra and vice versa. Calculated oscillator strength of quaternary alloys show presence of sufficient number of electrons in unoccupied conduction states beyond 27.0 eV during optical excitations. [ABSTRACT FROM AUTHOR]

With the recent establishment of atomically precise nanochemistry, capabilities toward programmable control over the nanoparticle size and structure are being developed. Advances in the synthesis of atomically precise nanoclusters (NCs, 1-3 nm) have been made in recent years, and more importantly, their total structures (core plus ligands) have been mapped out by X-ray crystallography. These ultrasmall Au nanoparticles exhibit strong quantum-confinement effect, manifested in their optical absorption properties. With the advantage of atomic precision, gold-thiolate nanoclusters (Au n (SR) m ) are revealed to contain an inner kernel, Au-S interface (motifs), and surface ligand (-R) shell. Programming the atomic packing into various crystallographic structures of the metal kernel can be achieved, which plays a significant role in determining the optical properties and the energy gap (E g ) of NCs. When the size increases, a general trend is observed for NCs with fcc or decahedral kernels, whereas those NCs with icosahedral kernels deviate from the general trend by showing comparably smaller E g . Comparisons are also made to further demonstrate the more decisive role of the kernel structure over surface motifs based on isomeric Au NCs and NC series with evolving kernel or motif structures. Finally, future perspectives are discussed., (© 2021 Wiley-VCH GmbH.)

Utilizing the tight-binding method, we investigate the electronic and optical properties of the zigzag hexagonal silicene quantum dots (ZHSQDs) subjected to a perpendicular magnetic field. The edge states emerge in the energy gap as the size of ZHSQDs increases. In the presence of spin–orbit coupling (SOC), the corresponding energy levels of edge states oscillate with magnetic flux. The reason is that the energy levels of silicene quantum dots are splitted in the presence of SOC. In addition, the optical absorption peak undergoes blue shift as the strength of SOC increases, and the optical absorption mainly occurs between the Landau levels in the presence of magnetic field. • The energy levels of edge states oscillate with the magnetic field due to SOC. • The optical absorption can be tuned by the SOC strength and the magnetic field. • Edge states emerge in the energy gap as the size of silicene quantum dots increases. [ABSTRACT FROM AUTHOR]

In order to examine the Zn doping impact on the electronic and optical behaviours of the host Cu 2 O material at various concentrations (x = 3.125%, 12.5%, and 25%) of Zn, we have performed first principles calculations. The computed electronic density of states of the pure bulk material Cu 2 O is established which corroborates the available previous experimental and theoretical reports. The Zn doped host material, made Cu 2 O to act as an n-type semiconductor, although the donor levels are formed nearby the lower conduction band. The bonding character showed that the orbital ordering disappeared on Cu atoms when cuprous oxide is doped with Zn. The interesting optical aspects, like the dielectric function, absorption coefficient, refractive index, optical conductivity, reflectivity, and electron energy loss function, are examined. We anticipate that this theoretical work will serve for further experimental realizations to engineer the electronic and optical behaviors of Cu 2 O doped with Zn for photocatalysis, sensors, and electronic device applications. • The Zn doping impact on the electronic and optical behaviours of the host Cu 2 O material is examined. • The Zn doped host material, turns Cu 2 O to behave as an n-type semiconductor. • The optical spectra illustrated that the Zn doping effect made the systems to absorb light in IR region. • The bonding character showed that an orbital ordering disappeared under the doping effect of Zn on the pure material. • The tunable optical features of Cu 2 O doped by Zn are useful for photocatalysis, and electronic device applications. [ABSTRACT FROM AUTHOR]

A novel gallium nitride (GaN) monolayer was investigated and predicted for the application in optoelectronic devices by first-principles calculations. The GaN monolayers with hydrogenation or fluorination are mechanically and thermodynamically stable except the half-fluorinated one. It is noted that their electronic structure with adjustable band gaps could be easily modified by chemical functionalization. The electronic and optical properties of half-hydrogenated GaN monolayer evidence narrowed band gap and enhancement of visible-light absorption. These results provide the guidance for fabrication of optoelectronic devices based on GaN monolayer. • Hydrogenated or fluorinated GaN monolayers are stable except the half-fluorinated one. • Hydrogen or fluorine atoms can easily modify the bandgap of GaN monolayer. • The visible-light absorption of GaN monolayer can be enhanced by half-hydrogenation. [ABSTRACT FROM AUTHOR]

• Debye model was used to get thermodynamic properties of WC phase ZnO. • B3LYP was used to get band and optical properties of WC phase ZnO. • Pressure induces a blue shift in recent predicted WC phase ZnO. • Equations were used to fit the relation between band gap, α (ω) and pressure. • We paved roads in applying WC phase ZnO in geophysics and material science. The present investigation highlights the structural, thermodynamic, electronic, and optical properties of WC (B h) phase ZnO calculated by means of first principles and Debye model approach. Acquired results revealed that pressure-induced phase transitions followed the sequence (B4 → WC → B2). The trend of thermodynamic properties with temperature and pressure has been discussed. Hybrid Functional (B3LYP) was employed to explore the bands and optical properties. The band gap under pressure is fitted well by a quadratic equation. Calculations demonstrate that an increase in band gap with increasing pressure leads to a blue shift in optical properties. The calculated band gap validates that the WC phase is an insulator, whereas the negative real part of dielectric function ε 1 (ω) indicates that it possesses metallic behaviour at around 21.9 & 23.5 eV. The relation between absorption constant and pressure is examined in detail. This exploration demonstrates the potential of WC phase ZnO for technological applications. [ABSTRACT FROM AUTHOR]

MoS 2 -based two-dimensional (2D) heterostructure photocatalysts have attracted increasing attention due to their prominent photocatalytic performance, but still suffer from weak visible light absorption and low solar-to-hydrogen conversion efficiency. Herein, we comprehensively investigate the structural and electronic properties of 2D MoS 2 /SnS heterostructure using first-principles calculations. It is found that the MoS 2 /SnS heterostructure is a stable interface and forms a type-II heterojunction, which definitely facilitates the spatial separation and migration of photoexcited electron-hole pairs under light irradiation. More importantly, a relatively small band gap (roughly 0.29 eV) enables its light absorption spectrum to cover the entire visible light region. Interestingly, the Mo atoms in the MoS 2 /SnS heterostructure would turn into catalytic active sites. As a result, constructing heterostructure of MoS 2 with SnS improves light absorption, accelerates the separation of electron-hole pairs, and activates the Mo atom at the basal plane, all of which could be beneficial to the photocatalytic activity. These results provide monolayer MoS 2 -based heterojunction photocatalysts and insightful understanding of their physical mechanism. • The MoS 2 /SnS heterostructure is a stable interface and forms a type-II heterojunction. • The type-II heterojunction facilitates the spatial separation and migration of electron-hole pairs under light irradiation. • Small band gap enables its light absorption spectrum to cover the entire visible light region. • The Mo atoms in the MoS 2 /SnS heterostructure would turn into catalytic active sites. [ABSTRACT FROM AUTHOR]

Inspired by the latest achievements of two-dimensional (2D) materials as gas sensors, we have performed ab-initio calculations to simulate the interactions between the explosive molecules (RDX, TEX, FOX-7 and TATB) and g-C 3 N 4 surfaces in order to exploit the potential applicability of g-C 3 N 4 as explosive sensor. The adsorption energies and measured distances of g-C 3 N 4 /explosive configurations indicate that the TATB molecule interacts strongly with g-C 3 N 4 and produces more number of extra peaks within the Fermi level region. The calculated sensitivity (S) test also demonstrates the superior sensitivity of g-C 3 N 4 towards TATB molecule. Keeping other semiconducting materials like graphene and boron nitride in perspective, our calculations show higher binding energies when explosive molecules are adsorbed on g-C 3 N 4 with appropriate charge transfer, representing better sensitivity for the latter. An increased work function is obtained when planar TATB and FOX-7 molecules are placed on the g-C 3 N 4 surface. Further, the sensitivity of g-C 3 N 4 for these explosive molecules is interpreted in terms of electronic and optical properties, where the density of states and absorption spectra show marked variations when explosive molecules are adsorbed on g-C 3 N 4 surface. The significant overlap between the interacting atoms of adsorbate and adsorbent in PDOS spectra represents the formation of chemical bonds at the interface region. Our calculations demonstrate the adsorption and reactivity processes that occur at the interface region, being useful to develop and design devices with extreme sensitivity for explosive detection. • The binding strength mainly depends upon the amount of charge transfer between explosive molecules and g-C 3 N 4 surface. • The adsorption energies and measured distances indicate that the TATB molecule interacts strongly with g-C 3 N 4. • The absorption spectra of g-C 3 N 4 /explosive complex show strong variations when compared to its pure counterpart. • The calculated sensitivity (S) test demonstrates the superior sensitivity of g-C 3 N 4 towards TATB molecule. [ABSTRACT FROM AUTHOR]

In this study, we used first principles calculations to investigate the influence of extracting the SnO (ML) monolayer, through electronic, optical and transport properties. Our simulation results of high optical transmission of SnO-ML comprehend the previously reported theoretical results. It shows around 96% optical transmission. These characteristics suggest that the SnO-ML is a potential material for optoelectronic and solar cell applications. In terms of thermoelectric properties, the electrical conductivity has been significantly improved at low temperature, the power factor and figure of merit are enhanced in SnO-ML. The materials' specifications considered that two-dimensional materials SnO-ML are better thermoelectric materials and may be efficient for thermoelectric energy conversion. • Applied the exact exchange-correlation potentials for treating different properties of SnO-Bulk and SnO-ML. • TB-mBJ potential is better for SnO-ML.Band gap is in reasonable agreement with experimentally reported. • The structural optimization and electronic properties of SnO-Bulk and SnO-ML are investigated. • The optical and thermoelectric properties for SnO-ML are significantly enhanced and the transparent properties can be still maintained and attained 95%. [ABSTRACT FROM AUTHOR]

We performed first-principle calculations based on density functional theory to investigate structural, electronic, optical, vibrational, and thermodynamic properties of the dopamine hydrochloride and Levodopa hydrochloride crystals. Our results showed a good agreement between the optimized structures and those determined previously by X-ray diffraction. The theoretical band gap of dopamine hydrochloride crystal was found to be indirect, whereas Levodopa hydrochloride showed a direct band gap. The calculated optical absorption of both crystalline structures occurs in the UV region, showing greater sensitivity to electromagnetic radiation with an energy of approximately 6 eV, and dielectric constant equal to 2.13 (2.15) for dopamine (Levodopa). • A quantum chemistry description of the dopamine and L-Dopa hydrochloride crystals. • We are using the DFT/GGA+TS in our simulation calculations. • The structural and electronic properties of the crystal structures are provided. • The thermodynamic, optical, and vibrational properties of the crystals are analyzed. [ABSTRACT FROM AUTHOR]

Two-dimensional materials have aroused enormous interests due to the novel physical properties and wide potential applications in optoelectronic devices. Monolayer or bilayer ZnO, as a typical two-dimensional metal-oxide, also exhibits astonishing properties. Motivated by the recent successful synthesis of Janus metal-oxide monolayer and bilayer, we have investigated the stability, electronic and optical properties of pristine and Janus F–ZnO–Cl monolayer and bilayer by the first-principles calculations. The results show that Janus F–ZnO–Cl monolayer and bilayer exhibit mechanical and dynamical stability without any imaginary modes of phonon spectra. Furthermore, the Janus functionalized will break the planar structure and form the buckled atomic layer in the monolayer and bilayer ZnO. Moreover, based on the HSE06 functional, Janus F–ZnO–Cl monolayer and bilayer exhibit the direct semiconductor characteristic, and the band gaps are narrowed from 3.374 eV to 2.563 eV, and from 3.185 eV to 1.022 eV, respectively. Upon Janus-functionalized, there are a large amount of charge (0.54 e) transfers from the ZnO layer to the functionalized species. In addition, Janus F–ZnO–Cl monolayer and bilayer could strongly absorb light in a wide range from the visible light to the infrared light at different level. The current findings open the possibilities for the application of ZnO-based material in optoelectronic devices. • Janus F–ZnO–Cl monolayer and bilayer are mechanically and dynamically stable. • Band gaps are reduced in Janus F–ZnO–Cl monolayer and bilayer in comparison with the pristine ones. • The hybridization between Cl-3 p and O-2 p states near the Fermi level plays a significant role in structural stability. • Janus F–ZnO–Cl monolayer and bilayer show good optical absorption from visible to ultraviolet regime. [ABSTRACT FROM AUTHOR]

• We have studied nine ternary sodium chalcogenides using first principles computations. • NaAsS 2 , NaSbS 2 , and NaSbSe 2 predicted to be stable in the monoclinic, C2/c , structure. • Remarkably high Seebeck coefficients exceeding 500 μ V/K are found. • Strong absorption observed in the visible-UV range for the three stable compounds. Ternary chalcogenides have been of recent investigation for applications in photovoltaic and thermoelectric devices. We study the structural, electronic, optical, and thermoelectric properties of nine ternary chalcogenides, NaAX 2 , where A represents pnictogens (As, Sb, and Te) and X represents chalcogens (S, Se, and Te). Calculations based on density functional theory yield the following results: (i) phonon dispersion curves predict three of the compounds, NaAsS 2 , NaSbS 2 , and NaSbSe 2 , to be dynamically stable in the monoclinic, C2/c , structure, (ii) the layered atomistic configuration causes the corresponding electronic and optical properties to display a high degree of anisotropy, (iii) A-X electronic bonding features vary significantly with structural distortions arising from atomic size mismatch, therefore directly influencing stability, (iv) strong absorption is observed in the stable compounds, with coefficients ranging from 10 4 to 10 5 cm−1 in the visible-UV range, and (v) remarkably high Seebeck coefficients exceeding 500 µ V/K, at carrier concentrations commonly achieved in such materials, are found. From these results, we conclude that NaAsS 2 , NaSbS 2 , and NaSbSe 2 are suitable candidates for both photovoltaic, particularly in tandem solar cells, and thermoelectric applications. Experimental synthesis and verification are suggested. [ABSTRACT FROM AUTHOR]

• Two stable Li-doped δ -graphyne structures exhibit metallic electronic structures. • Optical properties of three δ -graphynes exhibit strong anisotropic behaviour. • The reflectivity under parallel polarization is significant greater than the counterpart value under vertical polarization. • Three δ -graphyne structures have broad frequency photoresponse ranging from the zero frequency to ultra-violet regimes. First-principles calculations have been carried out to investigate the electronic and optical properties of lithium (Li)-decorated δ -graphynes. By calculating the total energy of different Li-decorated δ -graphyne structures, two most stable δ -graphyne structures are selected for this research, which are named δ 1-graphyne and δ 2-graphyne, respectively. Our results show that pristine δ -graphyne has two Dirac cones, while both δ 1-graphyne and δ 2-graphyne exhibit metallic character. The dielectric function, reflectivity, and absorption spectrum under different polarization conditions have been calculated to explore the optical properties of δ -graphyne, δ 1-graphyne, and δ 2-graphyne. The optical properties of three δ -graphyne structures all show strong anisotropic behaviour under different polarization directions. The reflectivity under E x and E y polarizations is significant greater than the counterpart value under the E z polarization. In the parallel polarization, three δ -graphyne structures all have high reflectivity in a wide frequency range. Besides, strong absorption coefficients of three δ -graphyne structures exist from far infrared to high-frequency range under E x and E y polarizations. Our results reveal that three δ -graphyne structures have broad frequency photoresponse ranging from zero frequency to ultraviolet regimes, suggesting that δ -graphyne is a promising material for optoelectronics applications. [ABSTRACT FROM AUTHOR]

The structural, electronic, and optical properties of inorganic CsPb(I1−xBrx)3 compounds were investigated using the full-potential linear augmented-plane wave (FP-LAPW) scheme with a generalized gradient approximation (GGA). Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and modified Becke–Johnson GGA (mBJ-GGA) potentials were used to study the electronic and optical properties. The band gaps calculated using the mBJ-GGA method gave the best agreement with experimentally reported values. CsPb(I1−xBrx)3 compounds were wide and direct band gap semiconductors, with a band gap located at the M point. The spectral weight (SW) approach was used to unfold the band structure. By substituting iodide with bromide, an increase in the band gap energy (Eg) values of 0.30 and 0.55 eV, using PBE-GGA and mBJ-GGA potentials, respectively, was observed, whereas the optical property parameters, which were also investigated, demonstrated the reverse effect. The high absorption spectra in the ultraviolet−visible energy range demonstrated that CsPb(I1−xBrx)3 perovskite could be used in optical and optoelectronic devices by partly replacing iodide with bromide. [ABSTRACT FROM AUTHOR]

• Fully hydrogenated InN monolayer is a semiconductor with indirect band gap of 2.591 eV. • Indirect-direct gap transition can occur in presence of biaxial strain and electric field. • Photocatalytic activity in the H–InN–H monolayer can be enhanced by strain or electric field. • Optical characteristics of the H–InN–H monolayer depends strongly on the biaxial strain. We investigate the electronic, photocatalytic and optical properties of a fully hydrogenated indium nitride H–InN–H monolayer under biaxial strain ε b and external electric field E using density functional theory. Our findings demonstrate that the H–InN–H monolayer is a semiconductor with an indirect energy gap of 2.591 eV. Under a biaxial strain or electric field, the indirect-direct band gap transition can occur and its band gap depends dramatically on the ε b and E. Our analysis of band edge alignment shows that the H–InN–H monolayer can possess photocatalytic activity for water splitting when an electric field or biaxial strain is applied. The optical characteristics of the H–InN–H monolayer depends greatly on the strain. The first optical gap of the H–InN–H monolayer is at the incident energy light of 3.320 eV and the tensile strain causes the first optical gap to shift towards the visible light region. [ABSTRACT FROM AUTHOR]

In this work, the electronic and optical properties of monolayer GaTe under biaxial strain and external electric field were investigated by density functional theory. Our calculated results indicate that the monolayer GaTe is an indirect-semiconductor with an energy gap of 1.41eV at equilibrium. Electronic properties of monolayer GaTe, especially the energy gap, depend greatly on the biaxial strain and external electric field. While the compressive strain slightly increases the energy gap, the tensile strain reduces quite rapidly the energy gap of the monolayer GaTe. In particular, semiconductor–metal phase transition can be observed when the external electric field was introduced. The GaTe monolayer strongly absorbs light in the ultraviolet region and the biaxial strain greatly changes its optical characteristics, especially the compression strain significantly increasing the absorption coefficient of the monolayer. Our results can provide more useful information for the prospect of application of the GaTe monolayer in next-generation optoelectronic devices. • Monolayer GaTe is an indirect-semiconductor with a moderate gap of 1.41eV at equilibrium. • Band gap of monolayer GaTe depends strongly on the biaxial strain. • Semiconductor–metal phase transition can be occurred in monolayer GaTe due to electric field. • Monolayer GaTe strongly absorbs light in the ultraviolet region. • Biaxial strain causes a significant shift in the first optical peaks of the GaTe monolayer. [ABSTRACT FROM AUTHOR]

In this paper, the structural stability, electronic, optical, mechanical, and thermal properties of diphenylacetylene-based graphyne (DPAG) nanosheet are investigated using first-principle calculations based on density functional theory (DFT). The absolute value of the calculated cohesive energy reveals that DPAG nanosheet is a structurally stable two-dimensional material. Also, in the results of phononic dispersion curves, the absence of imaginary frequencies confirms the dynamic stability of this novel material. In addition, the theoretical electronic band structure and density of states reveal the semiconducting nature of DPAG nanosheet. The optical analysis shows that the first absorption peaks of the imaginary and real parts of dielectric constants along the in-plane and out-of-plane polarizations of DPAG monolayer occur in the visible range of the electromagnetic spectrum. On the other hand, the DPAG nanosheet exhibits orthotropic elastic behavior with four independent constants comparable with the data of similar materials available in the literature. Moreover, DFT calculations of the lattice thermal conductivity of DPAG reveals an anomalously very low thermal conductivity of this nanosheet showing its perfect thermal non-conductivity. Our results provide deep insights into the potential applications of DPAG nanosheet for the design of new optoelectronic/nanoelectronic devices., (© 2021 IOP Publishing Ltd.)

Based on first-principles calculations, a novel family of two-dimensional (2D) IV-V compounds, XC 6 (X=N, P, As and Sb), is proposed. These compounds exhibit excellent stability, as determined from the cohesive energies, phonon dispersion analysis, ab initio molecular dynamics (AIMD) simulations, and mechanical properties. In this type of structure, the carbon atom is sp 2 hybridized, whereas the X (N, P, As and Sb) atom is nonplanar sp 3 hybridized with one 2p z orbital filled with lone pair electrons. NC 6 , PC 6 , AsC 6 and SbC 6 monolayers are intrinsic indirect semiconductors with wide bandgaps of 2.02, 2.36, 2.77, and 2.85 eV (based on HSE06 calculations), respectively. After applying mechanical strain, PC 6 , AsC 6 and SbC 6 monolayers can be transformed from indirect to direct semiconductors. The appropriate bandgaps and well-located band edge positions make XC 6 monolayers potential materials for photocatalytic water splitting. XC 6 family members also have high absorption coefficients (∼10 5  cm -1 ) in the ultraviolet region and higher electron mobilities (∼10 3  cm 2  V -1  s -1 ) than many known 2D semiconductors., (© 2021 Wiley-VCH GmbH.)

We studied the structural, electronic, and optical characters of SiS 2 , a new type of group IV-VI two-dimensional semiconductor, in this article. We focused on monolayer SiS 2 and its characteristic changes when different strains are applied on it. Results reveal that the monolayer SiS 2 is dynamically stable when no strain is applied. In terms of electronic properties, it remains a semiconductor under applied strain within the range from -10% to 10%. Besides, its indirect band-gap is altered regularly after applying a strain, whereas different strains lead to various changing trends. As for its optical properties, it exhibits remarkable transparency for infrared and most visible light. Its main absorption and reflection regions lie in the blue and ultraviolet areas. The applied uniaxial strain causes its different optical properties along the armchair direction and zigzag direction. Moreover, the tensile strain could tune its optical properties more effectively than the compressive strain. When different strains are applied, the major changes are in blue and ultraviolet regions, but only minor changes can be found in infrared and visible regions. So its optical properties reveal good stability in infrared and visible regions. Therefore, SiS 2 has a promising prospect in nano-electronic and nano-photoelectric devices., (© 2021 IOP Publishing Ltd.)

• We consider 14, 14, 18 Graphyne and Graphene as our study cases. • We calculate the electronic and optical properties of 14, 14, 18 Graphyne and Graphene and compare the results. • Both structures have zero electrical and optical bandgap and they are semi-metal. • Graphyne is more reflective and absorbent in visible range, while graphene acts better in the ultraviolet region. • The value of static dielectric constant for perpendicular polarization in Graphyne is larger than graphene, whereas it is lower for parallel one in Graphyne. In this paper, a 14, 14, 18 graphyne is considered and the electronic and optical properties are calculated within density functional theory combined with non-equilibrium Green's function. To better understanding of the features of the graphyne, the results are compared with graphene. Results demonstrate an improvement in absorption and reflectivity in visible region when graphyne is used, while graphene has better performance in the ultraviolet range. Also, the electronic band structure and density of states of the graphyne shows a zero-bandgap that leads to zero optical gap. Isotropic and anisotropic properties are obtained for graphene and graphyne in turn when optical properties are calculated for parallel and perpendicular polarizations. [ABSTRACT FROM AUTHOR]

• Monolayer GeSe is a semiconductor with a moderate indirect gap of 1.13 eV at equilibrium. • Semiconductor-metal phase transition occurs in monolayer GeSe at large compression biaxial strain. • Optical spectrum of monoalyer GeSe is highly anisotropy. • Monolayer GeSe possesses photocatalytic properties for water splitting at certain elongation of strain. In this work, we investigate the electronic and optical properties of monolayer GeSe and the possibility of enhancement the photocatalytic activities for the water splitting of monolayer GeSe through strain engineering using first-principles calculations. Our calculations indicate that monolayer GeSe is a semiconductor with a moderate indirect gap of 1.13 eV at equilibrium and we can control its band gap by biaxial strain. In the presence of biaxial strain ε b , the semiconductor-metal phase transition happens at large compressive strain of - 10 % and the indirect-direct gap transition occurs at ε b = 4 %. The optical spectrum of monolayer GeSe are highly anisotropic and biaxial strain can increase the absorption coefficient of monolayer GeSe up to about 6 × 10 5 cm−1. Our calculations demonstrate that monolayer GeSe possesses photocatalytic properties for water splitting at ε b = 5 % and we can enhance its photocatalytic activity by strain. [ABSTRACT FROM AUTHOR]

The effect of ZnO substrate on the structural and electronic properties of blue phosphorene were systematically investigated by first-principles calculations. The results show the band gaps of heterostructures are narrow than pure states and can be tuned sensitive by electric field. Zn pattern heterostructure is dynamically stable. In addition, E Γ and band gap can be tuned flexible which is reducing as strain increase and the structures turn from semiconductor to metal by compressive strain increasing, the optical properties indicate the optical absorption peak of the material is in the visible and ultraviolet region. • The effect of ZnO substrate on the structural and electronic properties of blue phosphorene were systematically investigated by PBE. • We build three blue P/ZnO monolayer heterostructures, Zn pattern has no imaginary frequency, which may be existence and stability. • Compared to pure states, the band gaps of structures are reduced and can be tuned by strain and electric-field for band gaps changing. • Have large absorption coefficient at wide spectral absorption range, which has potential applications as novel optical power limiting material. [ABSTRACT FROM AUTHOR]

In this work, we systematically investigate the electronic and optical properties of surface-functionalized GeC monolayer with F and Cl using density functional theory. Our calculations indicate that the surface functionalization of the GeC with F and C atoms leads to the disruption of the planar structure of the GeC monolayer and the surface-functionalized GeC monolayer has a low-bucking structure. At equilibrium, all four configurations of surface-functionalized GeC monolayer with F and Cl, i.e., F–GeC–F, F–GeC–Cl, Cl–GeC–F, and Cl–GeC–Cl, are direct semiconductors. Their band gaps vary from 2.839 eV to 3.175 eV which are calculated using Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Compared to the other configurations, the formation energy of F–GeC–F is the smallest, − 9. 097 eV , which implies that this configuration is the most likely to occur. We also used the Mulliken population analysis to estimate the internal charge distribution and transferred charge in the systems. The functionalization of the surface leads to the shifting the first optical gap of the material. The fully chlorination of GeC causes its absorption coefficient to increase significantly, up to 14. 912 × 1 0 4 cm−1 at the incident light energy of 13.173 eV. Besides, surface-functionalized GeC monolayer with F and Cl strongly absorbs light in the near ultraviolet region. Our calculation results provide detailed information on how to change the electronic and optical properties of monolayer GeC by surface functionalization, which has promising applications in opto-electronic devices. • All four configurations of surface-functionalized GeC monolayer with F and Cl are direct semiconductors. • Fully fluorinated F–GeC–F is the most likely to occur due to smallest formation energy. • The functionalization of GeC monolayer leads to the shifting the first optical gap of the material. • Surface-functionalized GeC monolayer with F and Cl strongly absorbs light in the near ultraviolet region. [ABSTRACT FROM AUTHOR]

The structural, electronic, and optical properties of metal (Si, Ge, Sn, and Pb) mono‐ and co‐doped anatase TiO2 nanotubes are investigated, to elucidate their potential for photocatalytic applications. It is found that Si‐doped TiO2 nanotubes are more stable than those doped with Ge, Sn, or Pb. All dopants lower the bandgap, except the (Ge, Sn) co‐doped structure, the decrease depending on the concentration and the type of dopant. Correspondingly, a redshift in the optical properties for all kinds of dopings is obtained. Even though a Pb mono‐ and co‐doped TiO2 nanotube has the lowest bandgap, these systems are not suitable for water splitting, due to the location of the conduction band edges, in contrast to Si, Ge, and Sn mono‐doped TiO2 nanotubes. On the other hand, co‐doping of TiO2 does not improve its photocatalytic properties. The findings are consistent with recent experiments, which show an enhancement of light absorption for Si‐ and Sn‐doped TiO2 nanotubes. [ABSTRACT FROM AUTHOR]

In search of novel, non-toxic and high performance materials for the use in quantum dot solar cells (QDSCs), we have investigated the effect of adatoms (nitrogen, boron and phosphorus) on carboxyl edge-functionalized graphene quantum dot (COOH-GQD) through the state-of-the-art first principles calculation based on density functional theory. The HOMO, LUMO and energy gaps are analysed in order to check the modulation in electronic properties by the foreign atom through hybrid functional B3LYP with 6-31G basis set. Binding mechanism, molecular electrostatic potential (MESP), and charge transfer are investigated to study the electron injection and charge separation in doped/undoped COOH-GQD. Optical properties show broad spectrum in the visible range favorable to harvest solar light. To envisage the application of adatom doped COOH-GQD in QDSC, the solar cell parameters such as open circuit voltage (V oc), Fill factor (FF), short circuit current density (J sc) and efficiency (η) are presented. The efficiency of COOH-GQD increases by 22–30% after the substitutional doping of nitrogen, boron and phosphorus. Maximum efficiency is achieved in case of phosphorus doping due to its more electron donating nature which will inject more electrons in TiO 2 surface. Our findings show that these new sensitizers based on GQD are promising candidates for QDSCs applications. Image 1 • Adatoms improves electronic, optical and photovoltaic properties of COOH-GQD. • The efficiency of COOH-GQD increases by 22–30% after the substitutional doping. • The efficiency of P-COOH-GQD is maximum due to the high electron injection in TiO 2. [ABSTRACT FROM AUTHOR]

Using the first principles calculations based on density functional theory (DFT), the effects of vertical compressive strain on the electronic and optical properties of the recently proposed 2D carbon allotrop namely penta-graphene are investigated. With the aim of validating our results, initially, the structural and the electronic properties of the pristine penta-graphene were regained. Our results display well-matched properties with the related works found in the literature. Our investigation into the electronic properties of the penta-graphene demonstrates that under vertical compressive strain conditions, an indirect to direct band gap transition occurs. Likewise, we also investigated its optical properties under strain conditions, showing that its optical behaviors match with its electronic ones. Consequently, the obtained results suggest 2D penta-graphene as a suitable material for designing electro-optic devices. • The electronic and optical properties of penta-graphene under buckling effects are investigated. • Under buckling effects, an indirect to direct band gap transition occurs. • The electronic and optical properties of the penta-graphene can be effectively tuned by buckling effects. • The obtained results suggest 2D penta-graphene as a suitable material for designing electro-optic devices. [ABSTRACT FROM AUTHOR]