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Here, using first-principles density functional theory (DFT), we investigated the structure cubic calculations of perovskite RbTaO3: bulk and surface (1 0 0). The Ta and O atoms in the TaO2-(1 0 0) termination appear to have a large atomic displacement (ΔZ) for the top and ninth layers, while the Rb atoms appear to have a minor value of ΔZ. In the RbO-(1 0 0), the Rb and O atoms in the first layer appear to have a large ΔZ, while the Ta atoms appear to have a major value of ΔZ in the second and eighth layers. We describe the thermodynamic formality used to evaluate the stability of RbTaO3 bulk, as well as RbO and TaO2-terminations. Our calculations showed that both the bulk system and the terminations are stable with the surrounding O atoms. The RbTaO3 bulk system appears to have semiconducting behavior with a band gap (Eg) of 2.25 eV. New RbO- and TaO2-terminations appeared half-metallic ferromagnetic (HMF) with a spin magnetic moment of 1.00 μβ. We found the Eg for RbO- and TaO2-terminations to be 2.25 and 2.40 eV, respectively. Also, the atomic populations (Q) and the variation (ΔQ) for (1 0 0)-RbTaO3 terminations were analyzed and compared with the bulk system. We calculated the optical properties of the RbTaO3 alloy and RbO- and TaO2-(1 0 0) surfaces. We found weak reflectivity, excellent optical conductivity, and higher absorption of incident energetic photons. Depending on the above properties, it is possible to use the bulk, RbO and TaO2 terminations in spintronics and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Although GaP, a III-V compound semiconductor, has been extensively utilized in the optoelectronic industry for decades as a traditional material, the inherent indirect bandgap nature of GaP limits its efficiency. Here, we demonstrate an indirect-to-direct bandgap transition of GaP through the formation of quantum shells on the surface of ZnS nanocrystals. The ZnS/GaP quantum shell with a reverse-type I heterojunction, consisting of a monolayer-thin GaP shell grown atop a ZnS core, exhibits a record-high photoluminescence quantum yield of 45.4% in the violet emission range (wavelength = 409 nm), validating its direct bandgap nature. Density functional theory calculations further reveal that ZnS nanocrystals, as the growth platform for GaP quantum shells, play a crucial role in the direct bandgap formation through hybridization of electronic states with GaP. These findings suggest potential for achieving direct bandgaps in compounds that are constrained by their inherent indirect energy gaps, offering a strategy for tailoring energy structures to significantly improve efficiencies in optoelectronics and photovoltaics. The indirect bandgap in GaP semiconductors limits its efficiency in optoelectronic applications. Here the authors realize a direct bandgap by forming ultrathin GaP quantum shells on ZnS nanocrystals, greatly enhancing luminescence efficiency. [ABSTRACT FROM AUTHOR]

Non-fullerene organic compounds are promising materials for advanced photovoltaic devices. The photovoltaic and electronic properties of the derivatives (TTBR and TTB1-TTB6) were determined by employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analyses using the M06/6-311G(d,p) functional. To enhance the effectiveness of fullerene-free organic photovoltaic cells, modifications were applied to end-capped acceptors by using strong electron-withdrawing moieties. The structural tailoring showed a significant electronic impact for HOMO and LUMO for all chromophores, resulting in decreased band gaps (3.184–2.540 eV). Interestingly, all the designed derivatives exhibited broader absorption spectra in the range of 486.365–605.895 nm in dichloromethane solvent. Among all derivatives, TTB5 was observed to be the promising candidate because of its lowest energy gap (2.54 eV) and binding energy (0.494 eV) values, along with the bathochromic shift (605.895 nm). These chromophores having an A–π–A framework might be considered promising materials for efficient organic cells. [ABSTRACT FROM AUTHOR]

Context: A novel 2D InN/GaN lateral heterostructure (LHT) was simulated by stitching monolayer of 2D InN and monolayer of 2D GaN. The structural stability, electronic structure, and optical properties were systematically investigated using first-principle calculations and by considering the effects of strain. The results indicated that the designed heterostructure has a direct bandgap of 2.26 eV which is further affected by applied biaxial strain. The bandgap of 2D InN/GaN lateral heterostructure decreases with the increase in biaxial strain, and tensile strain triggers a direct-to-indirect energy gap changeover at + 6%. Additionally, under compressive strain, heterostructure remains a direct bandgap semiconductor. Furthermore, the strain significantly affects the optical characteristics of lateral heterostructure. It has been noticed that the first optical absorption peak moves from 2.51 eV (ɛ = − 4%) to 1.40 eV (ɛ = 10%). Therefore, 2D InN/GaN lateral heterostructure provides an approachable way for utilizing in optoelectronic devices through the creation of in-plane lateral heterostructures. Methods: We performed all the computations using a self-consistent method based upon density functional theory. We used the PBEsol functional in the GGA to account for the exchange–correlation effects. We introduced a 10-Å vacuum region in the z-direction to avoid interaction between periodic images. We considered non-negligible weak dispersion correction in the lateral heterostructure using Grimme's DFT-D3 approach. In this study, we also computed the electrical and optical properties employing the local modified Becke-Johnson (lmBJ) exchange potential under meta-GGA functional to obtain more precise results. [ABSTRACT FROM AUTHOR]

HIV is one of the most threatening health conditions with a highly increasing rate, affecting millions of people globally, and from its time of discovery until now, its potential cure cannot be explicitly defined. This challenge of having no/low effective drugs for the subjected virus has called for serious attention in the scientific world of virus disease therapeutics. Most of these drugs yields low effectiveness due to poor delivery; hence, there is a need for novel engineering methods for efficient delivery. In this study, two nanomaterilas (graphene; GP, and fullerene; C60) were modelled and investigated with sulfur (S), selenium (Se), and oxygen (O) atoms, to facilitate the delivery of zidovudine (ZVD). This investigation was computationally investigated using the density functional theory (DFT), calculated at B3LYP functional and Gd3bj/Def2svp level of theory. Results from the frontier molecular orbital (FMO), revealed that the GP/C60_S_ZVD complex calculated the least energy gap of 0.668 eV, thus suggesting a favourable interactions. The study of adsorption energy revealed chemisorption among all the interacting complexes wherein GP/C60_S_ZVD complex (-1.59949 eV) was highlighted as the most interacting system, thereby proving its potential for the delivery of ZVD. The outcome of this research urges that a combination of GP and C60 modified with chalcogen particularly, O, S, and Se can aid in facilitating the delivery of zidovudine. [ABSTRACT FROM AUTHOR]

Hydrochar from waste biomass is a promising material for removing emerging contaminants (e.g., antibiotics) in water/soil environment. Abundant small-sized hydrochar particles (HPs) with a high content of reactive functional groups and high mobility are easily released into ecosystems through hydrochar applications. However, the photodegradation ability and corresponding structures of HPs are largely unknown, which hinder accurate estimation of the remediation effect of hydrochar in ecosystems. Herein, photodegradation performance of HP towards targeted norfloxacin (NOR, a typical antibiotic) under light irradiation (visible and UV light) were investigated after adsorption processes upon release into soil/water, and its reactive species and photoactive structures were clarified and compared with those of residual bulk hydrochar (BH) comprehensively. The results showed that: (1) photodegradation percentages of HPs were 4.02 and 4.48 times higher than those of BHs under UV and visible light, in which reactive species of both HPs and BHs were ·OH and ·O2−; (2) density functional theory (DFT) results identified that the main photoactive structure of graphitic-N decreased the energy gap (Eg) of HPs, and C=O, COOH groups improved electron donating ability of BHs; (3) well-developed graphitization structure of HP resulted from higher polymerization reaction was an significant photoactive structure involving its superior photodegradation ability relative to that of BH. The distinct heterogeneities of photodegradation ability in HP and BH and underlying photoactive structures provide an in-depth understanding of hydrochar application for removing emerging contaminants in soil/water environment. Identifying photoactive structures is helpful to predict photodegradation ability of hydrochar according to their abundance. Highlights: Photodegradation percentage of HP from hydrochar application was ~4 times superior to that of BH in degradation of NOR. Major reactive species of HPs and BHs (·OH and ·O2−) were generated from graphitic-N and C=O/COOH groups, respectively. Photoactivity of HPs superior to BHs was mainly generated from well-developed graphitization structure of former. [ABSTRACT FROM AUTHOR]

A new (C5H14N2)CoCl4 compound was synthesized by slow evaporation at room temperature. Asymmetric unit of this compound consists of one tetrahedral geometry [CoCl4]2- and one diprotonated organic cations. The structure consists of an alternation along the a-axis of organic-inorganic layers parallel to (a, b) plane. The inorganic layers built up of isolated tetrahedral [CoCl4]2-. Crystal packing is stabilized by electrostatic interactions and hydrogen bonds between cations and anions. Hirshfeld surface was conducted to investigate intermolecular interactions. Density Functional Theory (DFT) calculations of geometry optimization, vibrational frequencies, simulated UV-Visible spectrum, Frontier molecular orbitals analysis, nonlinear optical properties were made together with the experimental studies. Good agreement was found between theoretical and experimental results. In fact, the second hyperpolarizability value 〈γ〉 of compound (0.8665 × 10-36 esu) indicates that hydrogen bonds play an important role in the creation of crystal structure, its stability and in the enhancement of polarizability α and hyperpolarizability of crystal. Hence, the large 〈γ〉 value suggests that this compound is a Non-Linear Optical (NLO) material of interest and could be adopted in various optical applications. Energy gap indicates that our compound behaves as a semi-conductor material. In the other hand, the bioassay results showed that this structure exhibits significant antioxidant and antibacterial activities. [ABSTRACT FROM AUTHOR]

Context : Phographene and its family member structures are of the newly proposed semiconductors for detection of chemicals. That is, in this project, the potential of using α-phographene (α-POG) both for adsorption and detection of five types of the most important air pollutant gases containing SO2, AsH3, CF3H, NO2, and CO2 species were investigated. The results of the time dependent density functional theory (TD-DFT) calculations indicate that during the adsorption of NO2, and SO2 by the sorbent, big redshifts occur (up to 866.2 nm, and 936.5, respectively) resulting in considerable changes in the orbitals and the electronic structures of the systems. Moreover, the results of the thermodynamic calculations reveal that α-POG could selectively adsorb SO2, NO2, and AsH3 gases (with different orders), but it could not adsorb the two other gases.Finally, the outcome of the band gap calculations shows that between all mentioned gases, α-POG could selectively detect the presence of SO2, and then NO2; while, this nanosheet could not sense the existence of AsH3, CF3H, or CO2 gases. Methods: All of the calculations were carried out by using the Gaussian 03 quantum chemical package. In addition, the physiochemical parameters were extracted from the output files for further calculations. Studies on all saddle points and the following calculations were performed applying the B3LYP/6-311g(d,p) level of theory. [ABSTRACT FROM AUTHOR]

In the present work the effect of doping of P and Se on the reactivity and aromaticity of a few S,N-heteroacenes are discussed in the light of density functional theory (DFT) and conceptual density functional theory (CDFT). Reactivity parameters, hardness (η) and electrophilicity (ω), chemical potential (μ) and energy of the HOMO (highest occupied molecular orbital, EHOMO) are calculated to measure stability and reactive nature of the compounds. Doping of 'Se' in thiophene ring has no prominent effect on HOMO and LUMO energy (lowest unoccupied molecular orbital, ELUMO) of S,N-heteroacenes. Interestingly, there is a significant HOMO-LUMO energy gap reduction when 'N' of pyrrole ring is doped with 'P'. A steady decrease in the η values with respect to the size of the S,N-heteroacenes indicates the greater reactivity of larger acene systems. Nucleus independent chemical shift (NICS) advocates that doping of P exerts remarkable impact on the aromaticity of the concerned ring and overall aromaticity of the species. Time dependent density functional theory (TDDFT) study suggests decrease in absorption maxima with the increasing size of the oligomers. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) layered materials have illustrated prominent interest with various usages in optoelectronics, nanoelectronics, and solar cells. Numerous physical behaviors of 2D materials have been explored for a category of monolayer transition metal dichalcogenides (TMDCs). These involve molybdenum disulfide (MoS2), molybdenum diselenite (MoSe2), and MoSSe Janus monolayers that have gained remarkable interest because of their distinguished optoelectronic features. Particularly, the band gap transitions of these TMDC materials undergo from indirect band gap transition to direct one by reducing the dimension from the bulk-counterpart to their MoS2, MoSe2, and MoSSe monolayers, respectively. To this end, we conducted a comparative investigation and analysis of the electronic structure behaviors as well as optical spectra of MoS2, MoSe2, and MoSSe monolayers. The optical absorption spectra of these 2D materials are ranging between the infrared (IR) and visible regimes for MoS2, MoSe2, and MoSSe sheets and the absorption of light emerges between 1.6 and 1.8 eV, corresponding to their semiconducting character. These 2D materials are potential candidates for solar cells and optoelectronic applications. [ABSTRACT FROM AUTHOR]

This study employs density functional theory, utilizing plane wave ultra-soft pseudopotentials (PW-USPPs) within the generalized gradient approximation (GGA) and incorporating the Hubbard potential (GGA + U), to investigate the structural, electronic, and magnetic characteristics of Mn-doped 2D—WSe2 monolayers. The pristine WSe2 monolayer is identified as a nonmagnetic direct band gap semiconductor with a band gap of 1.55 eV. Upon substituting Mn for W in the WSe2 monolayer, the resulting structure exhibits enhanced stability, indicated by a negative formation energy. The Mn-doped monolayer-WSe2 adopts a semi-metallic nature, deviating from the nonmagnetic characteristics of the pristine 2D—WSe2, showcasing impurity bands dispersion near the Fermi level. The total magnetic moment within the nearest neighboring interactions of the Mn impurity atoms increases notably and it is attributed to the electron-correlation effect in the high spin state under the GGA + U approximation. However, this correlation effect proves insignificant on the total magnetic moment for the second nearest neighboring interactions, yielding consistent outcomes in both GGA and GGA + U approximations. The transition of ferromagnetic to antiferromagnetic states occurs within the temperature range of 400 K–450 K for low Mn-atom concentrations (below 12.5%), indicating long-range ferromagnetic ordering crucial for high-temperature 2D-diluted magnetic semiconductors. However, at high concentrations of impurity atoms, the temperature drops below room temperature (220 K in 22.2%) in the doped monolayer WSe2, showing weak magnetic interaction. Lastly, the optical properties of the doped system is studied by applying polarization in perpendicular and parallel directions to the plane of the monolayer. [ABSTRACT FROM AUTHOR]

The development of high-performance direct-Z Scheme heterojunctions as photocatalysts is the focus of current research, and it is also an effective way to improve the performance of photocatalysts. Based on this, we use density functional theory (DFT) to predict two-dimensional (2D) XSe2/SiH (X = Zr, Sn) van der Waals (vdW) heterojunction as a potential direct Z-scheme heterojunction photocatalyst. The results indicate that both heterojunctions exhibit a typical Type-II band edge arrangement. Furthermore, the small band gap and built-in electric field of the heterojunctions facilitate electronic transitions between the valence band (VB) and conduction band (CB), thereby increasing the probability of interlayer electron–hole (e−-h+) recombination within the heterojunction. This process is beneficial for the formation of direct-Z Scheme heterojunctions. In addition, the XSe2/SiH (X = Zr, Sn) heterojunction exhibits remarkable photogenerated electron and hole driving forces, along with exceptional light-trapping capabilities. Therefore, XSe2/SiH (X = Zr, Sn) heterojunction is a potential new photocatalyst. [ABSTRACT FROM AUTHOR]

Context: In the present work, we examined the sensing behavior of monolayer beta antimonide phosphorus (β-SbP) sheets towards toxic volatile organic compounds (VOCs) namely, 1,2-diethylbenzene and 2-ethyltoluene using density functional theory (DFT) method. At first, using cohesive energy structural stability of the monolayer β-SbP is confirmed. The calculated energy band gap value of monolayer β-SbP is 2.168 eV, which is a semiconductor. Furthermore, the adsorption properties of 1,2-diethylbenzene and 2-ethyltoluene on β-SbP are studied through key factors, such as adsorption energy, Mulliken charge transfer, and relative band gap variation. The adsorption energy clearly shows (− 0.335 to − 0.903 eV) that both 1,2-diethylbenzene and 2-ethyltoluene are physisorbed on β-SbP monolayer. Besides, Mulliken charge transfer falls in the range of − 0.465 to 0.933 e; this information clearly shows that the β-SbP monolayer is a potential candidate for sensing 1,2-diethylbenzene and 2-ethyltoluene molecules. Methods: The structural firmness including electronic and adsorption properties of 1,2-diethylbenzene and 2-ethyltoluene on β-SbP monolayer are investigated with the support of the DFT method. Particularly, the hybrid generalized gradient approximation (hybrid GGA) along with Beck's three-parameter + Lee–Yang–Parr (B3LYP) exchange–correlation functional is utilized for relaxing the β-SbP monolayer. In the present work, all calculations are performed using the Quantum Atomistic Tool Kit (ATK) simulation package. In the present work, we utilized β-SbP monolayer as a chief sensing element to detect 1,2-diethylbenzene and 2-ethyltoluene to safeguard humans from toxic environments. [ABSTRACT FROM AUTHOR]

This study involves the investigation of the double perovskite A2NbTbO6 (A = Ca, Sr, and Ba) using the PBE-GGA approximation under the quantum-based DFT (density functional theory) within the WIEN2k code. The materials A2NbTbO6 (A = Ca, Sr, and Ba) are cubic crystals with space group Fm3m-225 and non-magnetic behavior. The structural, electrical, optical, and thermoelectric characteristics of the given materials have been investigated. Band gap and density of state calculations are used to explain the electronic properties of the materials under study with the PBE-GGA approximation. The results made it abundantly evident that the materials are pure semiconductors with direct band gaps. Complex dielectric function, refractive index ƞ(ω), extinction coefficient K(ω), optical conductivity σ(ω), absorption coefficient α(ω), reflectivity R(ω), and loss parameter L(ω) are analyzed to explain the optical behavior of the materials. Charge carrier concentration (n), electrical conductivity (σ/t), Seebeck coefficient (S), power factor (PF), thermal conductivity (K/t), specific heat capacity (Cv), and magnetic susceptibility (χ) are investigated to find the material's thermal properties which show the ability of materials in green energy (eco-friendly) production devices and good candidates for optoelectronics especially for solar cell. The BoltzTraP code, which is part of the WIEN2k code, is used to calculate these properties. The cubic compounds Ca2NbTbO6, Sr2NbTbO6, and Ba2NbTbO6 have band gaps of 1.93 eV, 1.89 eV, and 1.87 eV, respectively and are direct band gap materials are confirmed from the band gap structures. By these calculations, all the characteristics are examined to produce new materials for sustainable devices and renewable energy applications like solar cells, and optoelectronics. [ABSTRACT FROM AUTHOR]

Double perovskite halides Cs2TlGaCl6 and Cs2TlGaBr6 are promising for photovoltaic applications due to their optoelectronic properties. The first-principles density functional theory (DFT) with the HSE06 hybrid functional was applied to systematically investigate their structural stability, electronic structure, optical absorption, and mechanical properties. The calculated tolerance and octahedral factors confirm stable crystal structures. The indirect band gaps of 2.50 eV (Cs2TlGaCl6) and 1.54 eV (Cs2TlGaBr6) are suitable for visible-light harvesting. Strong visible-light absorption and low reflectivity are observed. Elastic constant calculations based on the Voigt–Reuss–Hill approximation validate mechanical stability. The Spectroscopic Limited Maximum Efficiency (SLME) estimates promising photovoltaic efficiencies of 12.41% for Cs2TlGaCl6 and 29.73% for Cs2TlGaBr6 perovskite. These findings highlight the potential of Cs2TlGaCl6 and Cs2TlGaBr6 for low-cost, high-efficiency solar cells, warranting further experimental investigations. [ABSTRACT FROM AUTHOR]

We have explored the electronic and optical properties of the stanene–BeO heterostructure using density functional theory (DFT), including van der Waals interaction using the DFT-D3 correction method of Grimme. The heterostructure exhibits a significant band gap opening, with 93 meV (PBE) and 141 meV (HSE06) values. The impact of spin–orbit coupling (SOC) has also been studied, with PBE + SOC exhibiting a band gap of 55 meV and HSE06 + SOC exhibiting a band gap of 71 meV. Using the DFT-1/2 method, various optical parameters of BeO and Sn monolayer and Sn-BeO heterostructure were studied. The results show a strong red shift in the absorption coefficient, extinction coefficient, and reflectivity, with a prominent absorption peak in the near-UV and visible regions. A significant second harmonic generation peak of 8 × 104 pm V−1 was also obtained. The excellent optical properties of the heterostructure indicate its potential for use in future optoelectronic devices. [ABSTRACT FROM AUTHOR]

The adsorption attributes of methyl naphthalene and naphthalene molecules on P-Germanane sheets are explored based on the density functional theory method. The novel P-Germanane stability is established based on formation energy and phonon band spectrum. The stable P-Germanane exhibits a band gap of 3.944 eV. The calculated adsorption energy infers that methyl naphthalene and naphthalene are physisorbed on P-Germanane sheets. The charge transfer reveals that P-Germanane sheets behave as donors of electrons and target molecules behave as acceptors. The electronic attributes of P-Germanane sheets get altered owing to methyl naphthalene and naphthalene adsorption inferred from the band structure, PDOS spectrum, and electron density difference diagrams. We identified global minima position upon adsorption of 1-methylnaphthalene, and naphthalene on P-Germanane, which are named as bridge, octal, and tetra sites and adsorption attributes are explored in these sites. The adsorption energy and relative energy gap variation are noticed to be maximum for tetra site orientation of naphthalene on P-Germanane. The outcome exposes that P-Germanane sheets can be used as adsorption substrates for the detection of methyl naphthalene and naphthalene molecules. [ABSTRACT FROM AUTHOR]

This study examined the functionalization of graphene with easily ionizable elements, such as lithium, and subsequently its interaction with the biopolymer sodium alginate (SA), to highlight its potential for biomedical applications. Utilizing Density Functional Theory (DFT), the research comprehensively investigated the structural, electronic, and spectroscopic properties of these graphene-based composites. The electronic properties of functionalized graphene were investigated using DFT at the B3LYP/6-31G(d,p) level. Among the various configurations studied, graphene exhibited weak interaction with two lithium atoms, displaying the highest reactivity in terms of total dipole moment (TDM) at 5.967 Debye and a HOMO/LUMO energy gap (ΔE) of 0.748 eV. Electrostatic potential mapping revealed that graphene when enhanced with lithium and three units of SA, exhibited an augmented potential density on its surface, a finding corroborated by other investigated physical properties. Notably, the configuration of graphene/3SA/Li, with weak interaction occurring at two side carbons, demonstrated the highest reactivity with a TDM of 15.509 Debye and ΔE of 0.280 eV. Additionally, a shift in the spectral characteristics of graphene towards lower wavenumbers was observed as lithium and SA interacted with the graphene substrate. The PDOS plot for Graphene/3SA/Li, showed the highest contribution in the HOMO orbitals was equally from lithium, sodium, hydrogen, and oxygen, while the lowest contribution was from carbon. This computational analysis provides comprehensive insights into the functionalized graphene systems, aiding in their further development and optimization for practical biomedical use. [ABSTRACT FROM AUTHOR]

This research work's central focus is synthesizing a novel hybrid compound, formulated as [C6H9N2]2Sb2Cl8. This compound was prepared using the slow evaporation method and confirmed through single-crystal X-ray diffraction at 293 K. It crystallizes in the triclinic system with the centrosymmetric space group P 1 ¯ symmetry, and its unit cell (Z = 2). The intermolecular interactions have been studied using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing that the Cl–H contacts contribute the most to the surface area (63.6%). Computational studies that include geometry optimization and harmonic vibrational frequencies were performed using B3LYP method with GENECP set. Acceptable consistency was observed between calculated and experimental results. The assignment of wavenumbers was based on potential energy distribution (PED) using Vibrational Energy Distribution Analysis (VEDA) software. The optical band gap determined by UV–Visible spectroscopy is 3.48 eV for a direct allowed transition. Impedance spectroscopy was performed over a temperature range of 313 K to 413 K and a frequency range of 0.1 Hz to 1 MHz. The Nyquist plots indicated the presence of grain contributions. The conductivity study revealed that the synthesized material exhibits semiconductor behavior. A thermally activated conduction process was identified through the study of alternating conductivity, with a calculated activation energy of 1.104 eV. Additionally, the title compound exhibits a negative temperature coefficient of resistivity (TCR) with value of − 13%, suggesting the suitability of the sample for IR radiation detection applications. [ABSTRACT FROM AUTHOR]

Context: By using the DFT theory, the orbital energies of twenty-five ionic liquids were estimated. To comprehend their molecular stability and chemical reactivity, the orbital energy values, orbital energy gap (HOMO–LUMO energy gap), chemical hardness (η), chemical softness (S), electronegativity (χ), and electrophilicity index (ω) were computed. The interaction energies between all of the cations and anions under study were then computed and examined. Finally, using quantum chemical calculations, the molecular polarity of all 25 ionic liquids was examined using the sigma profile and sigma potential. Methods: Using the lowest orbital energy of the molecules, HF/6-31G* level of theory quantum chemical calculation were carried out using the MOLDEN and GAUSSIAN03 software. The B3LYP DFT approach produced a COSMO file that contained the species optimal SCD. [ABSTRACT FROM AUTHOR]

Context: The corrosion of mild steel is a significant issue in various industries, prompting the need for effective corrosion inhibitors. This study focuses on understanding the corrosion inhibition properties of organic compounds derived from isoxazole, namely series Iso(a), Iso(b), Iso(c), Iso(d), Iso(e), Iso(f), Iso(g), and Iso(h), which could have implications for materials science and industrial applications. By investigating the influence of different substitutions on these compounds, valuable insights can be gained into designing better corrosion inhibitors for practical use. Methods: Theoretical studies were conducted using density functional theory (DFT) with the B3LYP functional and the 6-31G (d,p) basis set. These calculations enabled the evaluation of various parameters including frontier orbital energies (EHOMO, ELUMO), energy gap (∆E), electronegativity (χ), absolute hardness (η), softness (σ), fraction of transferred electrons (∆N), as well as local properties such as natural atomic populations and Fukui indices. Additionally, molecular dynamics simulations were performed to study the adsorption behavior of the inhibitors on the surface of Fe (110). The simulations were conducted using Materials Studio version 8.0 software package using COMPASS force field to understand the impact of different functional groups on the inhibitors before and after adsorption on the iron surface. [ABSTRACT FROM AUTHOR]

Context: Due to the widely known positive contributions of the quinoxaline group in organic semiconductors, we conducted a fully computational study using quantum mechanical methods to investigate the effect of quinoxaline in the electron acceptor unit with the combination of different chalcogen atoms on the band gap of a series of donor–acceptor-donor type conjugated polymers. Using density functional theory, we mainly calculated the electronic band gap values of the structures containing four different chalcogen atoms (O, S, Se, and Te) in the electron donor and acceptor units. While chalcogendiazoloquinoxaline groups were used as the electron acceptor units, furan, thiophene, selenophene, and tellurophene were used as the donor units. Our theoretical results showed that the use of heavy chalcogen atoms in both donor and acceptor units resulted in a low band gap. Besides this, the effect of heavy chalcogen atoms used in the electron donor units is much more pronounced compared to the ones used in the acceptor units. More importantly, our findings proved that the inclusion of the chalcogendiazoloquinoxaline group instead of benzochalcogenadiazole as the acceptor unit significantly decreases the electronic band gap of the conjugated polymer. The lowest band gap was found to be 0.10 eV for the 4,9-di(tellurophen-2-yl)-[1,2,5]telluradiazolo[3,4-g]quinoxaline polymer. Methods: Conformational analysis of the monomers and their corresponding oligomers was performed at the B3LYP/LANL2DZ level of theory. Then, long-range corrected hybrid functional LC-BLYP in a combination with the LANL2DZ basis set was utilized for the calculation of electronic properties and HOMO and LUMO energy gaps of monomers and oligomers through the reoptimization of the lowest energy conformers obtained from the B3LYP/LANL2DZ calculations in the previous step. All energy minimum structures were confirmed through vibrational frequency analysis at both calculation levels. The Gaussian 09 rev. D.01 software was used for all calculations, and GaussView 5.0.9 for visualizations. [ABSTRACT FROM AUTHOR]

This study conducts a comprehensive investigation into the electronic characteristics and optical behaviour of hetero-ring doped graphene quantum dots (GQDs) using a combination of density functional theory and many-body perturbation methods. The focus is on exploring a novel doping mechanism involving the interplay between the type and positioning of dopant rings, specifically Morpholone, Oxazole, and Thiazole rings. The doping process significantly alters the structural, electronic, and optical properties of the pristine GQD. Structural distortions are observed in the doped nanostructures due to variations in atomic radii and electronegativity among C, O, N, and S atoms. The HOMO-LUMO (H–L) band gap and optical gap exhibit reduction upon doping. Additionally, the absorption spectra of the doped nanostructures shift to lower energy levels compared to the pristine GQD. This finding, coupled with high binding energies and reduced singlet-triplet splitting, provide insights into the photophysical processes within each studied structure, suggesting potential applications. [ABSTRACT FROM AUTHOR]

The pursuit of new materials with tailored properties is essential for advancing technology. This research focuses on GaXF3 (X = Se, Si) fluoroperovskites, utilizing the density functional theory approach. The study begins by assessing structural properties, revealing stable configurations for both compounds. The results from phonon calculations confirm the thermodynamic stability of the compounds. The relationship between elastic constants, confirms their mechanical stability. Elasticity analysis using the IRelast package indicates their resilience, anisotropic characteristics, and mechanical stability. Electronic properties, including band structure, density of states, and electronic band gaps, show that both materials have a metallic nature. Additionally, optical properties, such as dielectric constants, absorption coefficients, and refractive indices, are explored, providing insights into their interactions with light for optoelectronic applications. Optical property calculations for both GaSeF3 and GaSiF3, indicate their potential suitability for use in optoelectronic devices, particularly LEDs, due to their absorption within the UV–Vis range. These results encompass properties such as reflectivity, refractive index, and absorption coefficients, indicating their relevance to potential applications in optoelectronic devices. These findings enhance our understanding of these materials and lay the groundwork for future advancements in advanced materials science. [ABSTRACT FROM AUTHOR]

First principles calculations of the structural, electronic and optical properties of GaSb, InSb and their ternary Ga 1 - x In x Sb alloys (x = 0.25, 0.50 and 0.75) have been performed using the full-potential linear muffin-tin orbital (FP-LAPW) method within density functional theory (DFT). The generalized gradient approximation and modified Becke and Janson functional with local density approximation (mBJ–LDA) are utilized for the treatment of exchange and correlation potentials. The results show the calculated lattice constants increase linearity with increasing the In concentration. The electronic band structure indicates that these alloys are direct band gap semiconductors for all the values of x and the band gap decreases as x increases from x = 0 to x = 1. The results also show that the there is a non-linear dependence of the band gap on composition x in Ga 1 - x In x Sb alloys. Regarding optical properties, the real and imaginary parts of the dielectric function have been calculated. The results show that the static dielectric constant increases with increase in concentration of In, consistent with reduction in energy band gap. The onset point and major peaks in the imaginary parts of the dielectric function spectra are identified for the Ga 1 - x In x Sb alloys and shown that they are related to the corresponding band gap values. The results also show that for energy values higher than ≅ 4 eV, the electromagnetic wave transition through Ga 1 - x In x Sb alloys is nearly zero. [ABSTRACT FROM AUTHOR]

Sequencing the DNA nucleobases is essential in the diagnosis and treatment of many diseases related to human genes. In this article, the encapsulation of DNA nucleobases with some of the important synthesized chiral (7, 6), (8, 6), and (10, 8) carbon nanotubes were investigated. The structures were modeled by applying density functional theory based on tight binding method (DFTB) by considering semi-empirical basis sets. Encapsulating DNA nucleobases on the inside of CNTs caused changes in the electronic properties of the selected chiral CNTs. The results confirmed that van der Waals (vdW) interactions, π-orbitals interactions, non-bonded electron pairs, and the presence of high electronegative atoms are the key factors for these changes. The result of electronic parameters showed that among the CNTs, CNT (8, 6) is a suitable choice in sequencing guanine (G) and cytosine (C) DNA nucleobases. However, they are not able to sequence adenine (A) and thymine (T). According to the band gap energy engineering approach and absorption energy, the presence of G and C DNA nucleobases decreased the band gap energy of CNTs. Hence selected CNTs suggested as biosensor substrates for sequencing G and C DNA nucleobases. [ABSTRACT FROM AUTHOR]

Context: The electronic properties and optical properties of Cr-doped monolayer WS2 under uniaxial compressive deformation have been investigated based on density functional theory. In terms of electronic structure properties, both intrinsic and doped system bandgaps decrease with the increase of compression deformation, and the values of the bandgap under the same compression deformation after Cr doping are reduced compared with the corresponding intrinsic states. When the compressive deformation reaches 10%, both the intrinsic and doped system band gaps are close to zero. New electronic states and impurity energy levels appear in the WS2 system when doped with Cr atoms. For the optical properties, the calculation and analysis of the dielectric function under each deformation regime of monolayer WS2 show that the compression deformation affects the dielectric function, and when the compression deformation is 10%, the un-doped and Cr-doped regimes show a decrease in ε1(ω) compared to the compression deformation of 8%. For each deformation system, the peak reflections occur in the ultraviolet region. Near the position where the second peak of the absorption spectrum appears, it can be seen that the ability of each system to absorb light gradually decreases with the increase of the amount of deformation and appears to be red-shifted to varying degrees. Methods: This study follows the initial principles of the density functional theory framework and is based on the CASTEP module of Materials-Studio software GGA and PBE generalizations are used to perform computations such as geometry optimization of the model. We have calculated the energy band structure of monolayer WS2 with intrinsic and compressive deformations of 2% and 4% using PBE and HSE06, respectively. The band gap values calculated using PBE are 1.802 eV, 1.663 eV, and 1.353 eV, respectively, and the band gap values calculated with HSE06 are 2.267 eV, 2.034 eV, 1.751 eV. The results show that the bandgap values calculated by HSE06 are significantly higher than those calculated by PBE, but the bandgap variations calculated by the two methods have the same trend, and the shape characteristics of the energy band structure are also the same. However, it is worth noting that the computation time required for the HSE06 calculation is much longer than that of the PBE, which is far beyond the capability of our computer hardware, and the purpose of this paper is to investigate the change rule of the effect of deformation on the bandgap value, so to save the computational resources, the next calculations are all calculated using the PBE. The Monkhorst–Pack special K-point sampling method is used in the calculations. The cutoff energy for the plane wave expansion is 400 eV, and the K-point grid is assumed to be 5 × 5 × 1. Following geometric optimization, the iterative precision converges to a value of less than 0.03 eV/Å for all atomic forces and at least 1 × 10−5 eV/atom for the total energy of each atom. The vacuum layer's thickness was selected at 20 Å to mitigate the impact of the interlayer contact force. [ABSTRACT FROM AUTHOR]

Context: The 2D AlN/BN planer heterostructure is a promising wide band gap semiconductor, but systematic studies of its bandgap and optical characteristics under applied strain are scarce. Here, the engineering property of 2D AlN/BN comprising bandgap nature transition and optical absorption capability (from unstrained to strained) have been investigated using density functional theory calculations. The formation energy calculations confirm the stability of the simulated nanoheterostructure. The electronic band structure calculations demonstrate that nanoheterostructure is an indirect bandgap material with a large bandgap of 5.26 eV, which can be modified effectively by applying strain. According to the calculations, the transition from indirect to direct band gap behavior has been observed at +15% biaxial strain with 2.71 eV band gap energy. Meanwhile, calculations for optical absorption and dielectric function reveal that the system has significant absorption peaks in the ultraviolet region which are very sensitive to applied strain. As strain increases, the first absorption peaks are shifted towards a lower energy range from 5.73 eV (Ꜫ= 0 %) to 3.76 eV (Ꜫ = +15%), which features an enhancement of optical absorption for solar and solar-blind regions. Furthermore, we determined that the band edge positions in 2D AlN/BN straddled the water redox potential under strain, indicating its effectiveness as a proficient photocatalyst. These characteristics make 2D AlN/BN planer nanoheterostructure a promising candidate for applications in optoelectronics and photocatalytic water splitting performance. Methods: First principles computations based on density functional theory were employed to carry out all the calculations with a self-consistent approach. For solving the Kohn-Sham equations, the first principles dependent full-potential linearized augmented plane wave scheme were adopted. For addressing the exchange-correlation effects, the generalized gradient approximation of PBEsol functional was used. To prevent interaction between the periodic images, we have inserted a vacuum region of 10 Å in the z-direction. Non-negligible weak dispersion corrections in nanoheterostructure were considered by using the DFT-D3 method of Grimme's. The locally modified Becke-Johnson (lmBJ) exchange potential has also been applied to compute electronic and optical properties in this research to obtain more accurate information. [ABSTRACT FROM AUTHOR]

Context: Two-dimensional (2D) nanoheterostructures of materials, integrating various phase or materials into a single nanosheet have stimulated large-scale research interest for designing novel two dimensional devices. In contemporary analysis present work, we examined the structural and electronic properties of the isolated 2D BN and GaN monolayers. We have investigated the structural stability and optoelectronic and photocatalytic response of the g-GaN/BN nanoheterostructure along with its response to strain. Nanoheterostructure g-GaN/BN is predicted to be a direct bandgap semiconductor with wide gap of 4.45 eV, whose value can be effectively modulated by applied strain ( ϵ) , ranging from 4.55 (ϵ = − 4%) to 3.58 eV (ϵ = 8%). We also discovered that the tensile strain of 8% can substantially tune the direct bandgap of nanoheterostructure to indirect band gap nature. Even more important, the biaxial tensile strain engineering accentuates an enhancement of optical absorption in the UV region, broadening the light harvesting of the g-GaN/BN nanoheterostructure with the shifting of first absorption peak from 4.64 (ϵ = − 4%) to 3.71 eV (ϵ = 8%). Furthermore, strain-tuned band edge potentials arrangement perfectly fits the water reduction and oxidation redox potentials. Our findings portend that the g-GaN/BN nanoheterostructure has application in prospective nanoscale optoelectronic devices and photocatalytic hydrogen evolution system. Methods: First principles calculations in this study are performed using density functional theory. Generalized gradient approximation within PBEsol functional employed to address the electron–electron exchange–correlation effects. For avoiding periodic interactions between the layers, we have inserted a vacuum region of thickness 10 Å in the z-direction. For ensuring the convergence accuracy of the computed results, convergence criteria of the iteration process is set to be 0.0001 eV. Local modified Becke–Johnson, a semi local functional, is applied for calculating electronic and optical properties for more accuracy of results. As in layered 2D nanoheterostructure, a factual depiction of the van der Waals interactions cannot be provided by conventional DFT techniques. Accordingly, in order to incorporate these interactions, we had employed the dispersion correction method of Grimme's. [ABSTRACT FROM AUTHOR]

Context: In this paper, the optimum coverage of 4.44% and the optimum adsorption sites were determined for the Be3N2 adsorption system of O atoms at different coverages based on density functional theory. The electronic and optical properties of the model were investigated by applying bending deformation to the model at these coverage and adsorption sites. Adsorption of O atoms disrupts the geometrical symmetry of Be3N2, resulting in orbital rehybridization and lowering its band gap. Bending deformation causes the band gap of the adsorbed O atom structure of Be3N2 to first increase and then decrease, resulting in the modulation of its band gap. With increasing bending deformation, the adsorbed system is redshifts, and the degree of redshift increases with increasing bending deformation. Methods: All calculations in this paper were performed using the first-principles-based CASTEP module of Materials Studio (MS). The generalized gradient approximation (GGA) plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof (PBE) Perdew et al. Phys Rev Lett 77:3865, 1996 generalized functional were used in the geometry optimization and calculation process to calculate the exchange–correlation potential between electrons. The effect of coverage on the electronic and optical properties of the Be3N2-adsorbed O atom system was investigated by adsorbing different numbers of O atoms on a monolayer of Be3N2. The Be3N2 protocell contains two N atoms and three Be atoms with a space community of P6/MMM (No.191). The original cell was expanded 3 times along the direction of the base vectors a and b in the Be3N2 plane to create a 3 × 3 × 1 monolayer Be3N2 supercell system. A vacuum layer of 15 Å is set in the direction of the crystal plane of the vertical monolayer Be3N2 supercell to eliminate interactions between adjacent layers. In the overall energy convergence test of the Be3N2 supercell, the plane wave truncation energy was set to 500 eV, and the energy difference between the calculations given in the literature Reyes-Serrato et al. J Phys Chem Solids 59:743-6, 1998 using 550 eV was less than 0.01 eV, verifying the reliability of the data at a truncation energy of 500 eV. The Monkhorst–Pack special k-point sampling method Monkhorst et al. Phys Rev B 13:5188, 1976 was used in the structural calculations, and the grid was set to 3 × 3 × 1. The geometric optimization parameters are set as follows: the self-consistent field iteration convergence criterion is 2.0 × 10−6 eV, and the iterative accuracy convergence value is not less than 1.0 × 10−5 eV/atom for the total force of each atom and less than 0.03 eV/Å for all atomic forces. In addition the high-symmetry k-point path is taken as Γ(0,0,0) → M(0,0.5,0) → K(− 1/3,2/3,0) → Γ(0,0,0) Chen et al, AIP Adv 8:105105, 2018. [ABSTRACT FROM AUTHOR]

Context: The electronic, discrete water solvation, and vibrational properties of zwitterionic sulfanilic acid were thoroughly investigated using periodic and non-periodic DFT approaches. The periodic-DFT results, obtained by employing the PBE-TS functional (Perdew-Burke-Ernzerhof (PBE) functional with the Tkatchenko and Scheffler (TS) dispersion correction) were first presented in order to analyze the band structures of the studied crystal. An attentive reading of the predicted band structures has shown three lowest gap energies calculated at 4.23, 4.24, and 4.29 eV arising from the Γ→Γ, Γ→Z, and Γ→S transitions, respectively. Then, non-periodic calculations were carried out, at the B3LYP-D3 level of theory (B3LYP functional with the D3 Grimme dispersion correction) in order to optimize the sulfanilic acid-(H2O)10 complex. Starting from the optimized structure, non-covalent interaction calculations were performed and the H-bonding, van der Waals, and steric effect interactions were identified. Finally, the PBE-TS calculations were strengthened by conducting anharmonic B3LYP-D3 calculations in order to achieve a complete decryption of the experimental IR spectrum of sulfanilic acid. The spectral analysis is not limited only to the interpretation of both the NH/CH stretching and fingerprint regions but also extended to the 1800–2600 cm−1 region, which is characterized by a strong anharmonic effect. In the latter wavenumber region, the large experimental IR band centered at 1937 cm−1 is reproduced theoretically employing the anharmonic B3LYP-D3 calculations. The similarity of this band with those usually considered as a fingerprint of zwitterionic amino acids is observed, and its origin is elucidated theoretically. In the vibrational spectroscopy field, the calculations presented in this study are probably the most appropriate for achieving vast analysis and accurate assignments of vibrational spectra of hydrogen bonding compounds recorded in the solid state. Method: The periodic and non-periodic calculations were conducted within the Density Functional Theory (DFT) using the Generalized Gradient Approximation (GGA) at the PBE-TS level of theory and B3LYP-D3 functional with the 6-311++G(d,p) basis set, respectively. The PBE-TS and B3LYP-D3/6-311++G(d,p) calculations were performed using the CASTEP and Gaussian 09 programs, respectively. In addition, The non-covalent interactions were calculated by the Multiwfn 3.8 software. The obtained results for different calculations were visualized by employing the visualization tools in Materials Studio, GaussView, VMD, and Gnuplot programs. [ABSTRACT FROM AUTHOR]

This research employs the FP-LAPW approach within density functional theory to investigate the structural, optical, electronic, and elastic features of GaXCl3 (X = Be, Ca) chloroperovskites. The computational analysis, incorporating Birch Murnaghan curve optimization for structural stability and IRelast for elastic constants, affirms the anisotropic, ductile, and mechanically stable nature of both GaBeCl3 and GaCaCl3. Electronic characteristics are examined using the Tb-mBJ potential, revealing GaBeCl3 as semiconducting with a 3.03 eV direct band gap (M-Γ) and GaCaCl3 as insulating with a 4.90 eV direct band gap (X–X). Total and partial densities of states (TDOS and PDOS) provide insights into the contributions of elemental states to the band structure. Optical features explored up to 13 eV emphasize significant peaks in the spectra based on observed electronic structures. These findings contribute to a more thorough comprehension of the physical characteristics of chloroperovskites based on Gallium, paving the way for their utilization in optoelectronic devices and as insulating materials. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of the crystal structure, electronic characteristicsmechanical and optical responses of CsPbBr3, CsPbCl3, CsPbI3 and Mg+2-doped at the Pb+2-site perovskites. Our investigation is based on density functional theory calculations, shedding light on their potential applications in solar cells. Moreover, they exhibit characteristics of a direct bandgap nature, with computed bandgap values of 1.61 eV (CsPbI3), 1.58 eV (0.25 Mg+2), 1.49 eV (0.50 Mg+2), 1.28 eV (0.75 Mg+2) for the first material; 1.86 eV (CsPbBr3), 1.55 eV (0.25 Mg+2), 1.09 eV (0.50 Mg+2), 0.94 eV (0.75 Mg+2) for the second material; and 2.28 eV (CsPbCl3), 2.34 eV (0.25 Mg+2), 2.27 eV (0.50 Mg+2), and 3.52 eV (0.75 Mg+2) for the third material, respectively. Notably, these compounds display characteristics of direct bandgap behavior. The valence band maximum is primarily derived from halide p orbitals, forming hybrid states with Pb-5s states. It is discerned that alterations in the lattice parameter and volume of the pure and doped CsPb1 − xMgxl3, CsPb1 − xMgxBr3, and CsPb1 − xMgxCl3 materials unit cell lead to proportional modifications in the band gap values. The achieved results show that the systems can exist stably in terms of mechanical as well as dynamical stabilities, and CsPb1 − xMgxl3, CsPb1 − xMgxBr3, and CsPb1 − xMgxCl3 (0, 0.25, 0.50, and 0.75) materials structures have anisotropy and ductile elastic responses. These materials exhibit excellent photon absorption capabilities owing to their narrow bandgaps, as evidenced by their distinctive optical properties. The real (ε1 (ω)) and imaginary (ε2 (ω)) components of their dielectric functions indicate a remarkable capacity to effectively capture and retain absorbed energy. Specifically, in the case of pure and doped CsPb1 − xMgxl3, CsPb1 − xMgxBr3, and CsPb1 − xMgxCl3, these characteristics make them highly promising for utilization in solar cells and energy storage applications. It is remarkable to report that, notably, at elevated photon energy levels, these materials also display super luminescent behavior, thus further expanding their potential for advanced optoelectronic applications. [ABSTRACT FROM AUTHOR]

Context: The electronic properties and optical properties of Cr-doped monolayer WS2 under uniaxial compressive deformation have been investigated based on density functional theory. In terms of electronic structure properties, both intrinsic and doped system bandgaps decrease with the increase of compression deformation, and the values of the bandgap under the same compression deformation after Cr doping are reduced compared with the corresponding intrinsic states. When the compressive deformation reaches 10%, both the intrinsic and doped system band gaps are close to zero. New electronic states and impurity energy levels appear in the WS2 system when doped with Cr atoms. For the optical properties, the calculation and analysis of the dielectric function under each deformation regime of monolayer WS2 show that the compression deformation affects the dielectric function, and when the compression deformation is 10%, the un-doped and Cr-doped regimes show a decrease in ε1(ω) compared to the compression deformation of 8%. For each deformation system, the peak reflections occur in the ultraviolet region. Near the position where the second peak of the absorption spectrum appears, it can be seen that the ability of each system to absorb light gradually decreases with the increase of the amount of deformation and appears to be red-shifted to varying degrees. Methods: This study follows the initial principles of the density functional theory framework and is based on the CASTEP module of Materials-Studio software GGA and PBE generalizations are used to perform computations such as geometry optimization of the model. We have calculated the energy band structure of monolayer WS2 with intrinsic and compressive deformations of 2% and 4% using PBE and HSE06, respectively. The band gap values calculated using PBE are 1.802 eV, 1.663 eV, and 1.353 eV, respectively, and the band gap values calculated with HSE06 are 2.267 eV, 2.034 eV, 1.751 eV. The results show that the bandgap values calculated by HSE06 are significantly higher than those calculated by PBE, but the bandgap variations calculated by the two methods have the same trend, and the shape characteristics of the energy band structure are also the same. However, it is worth noting that the computation time required for the HSE06 calculation is much longer than that of the PBE, which is far beyond the capability of our computer hardware, and the purpose of this paper is to investigate the change rule of the effect of deformation on the bandgap value, so to save the computational resources, the next calculations are all calculated using the PBE. The Monkhorst–Pack special K-point sampling method is used in the calculations. The cutoff energy for the plane wave expansion is 400 eV, and the K-point grid is assumed to be 5 × 5 × 1. Following geometric optimization, the iterative precision converges to a value of less than 0.03 eV/Å for all atomic forces and at least 1 × 10−5 eV/atom for the total energy of each atom. The vacuum layer's thickness was selected at 20 Å to mitigate the impact of the interlayer contact force. [ABSTRACT FROM AUTHOR]

Context: In this paper, the optimum coverage of 4.44% and the optimum adsorption sites were determined for the Be3N2 adsorption system of O atoms at different coverages based on density functional theory. The electronic and optical properties of the model were investigated by applying bending deformation to the model at these coverage and adsorption sites. Adsorption of O atoms disrupts the geometrical symmetry of Be3N2, resulting in orbital rehybridization and lowering its band gap. Bending deformation causes the band gap of the adsorbed O atom structure of Be3N2 to first increase and then decrease, resulting in the modulation of its band gap. With increasing bending deformation, the adsorbed system is redshifts, and the degree of redshift increases with increasing bending deformation. Methods: All calculations in this paper were performed using the first-principles-based CASTEP module of Materials Studio (MS). The generalized gradient approximation (GGA) plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof (PBE) Perdew et al. Phys Rev Lett 77:3865, 1996 generalized functional were used in the geometry optimization and calculation process to calculate the exchange–correlation potential between electrons. The effect of coverage on the electronic and optical properties of the Be3N2-adsorbed O atom system was investigated by adsorbing different numbers of O atoms on a monolayer of Be3N2. The Be3N2 protocell contains two N atoms and three Be atoms with a space community of P6/MMM (No.191). The original cell was expanded 3 times along the direction of the base vectors a and b in the Be3N2 plane to create a 3 × 3 × 1 monolayer Be3N2 supercell system. A vacuum layer of 15 Å is set in the direction of the crystal plane of the vertical monolayer Be3N2 supercell to eliminate interactions between adjacent layers. In the overall energy convergence test of the Be3N2 supercell, the plane wave truncation energy was set to 500 eV, and the energy difference between the calculations given in the literature Reyes-Serrato et al. J Phys Chem Solids 59:743-6, 1998 using 550 eV was less than 0.01 eV, verifying the reliability of the data at a truncation energy of 500 eV. The Monkhorst–Pack special k-point sampling method Monkhorst et al. Phys Rev B 13:5188, 1976 was used in the structural calculations, and the grid was set to 3 × 3 × 1. The geometric optimization parameters are set as follows: the self-consistent field iteration convergence criterion is 2.0 × 10−6 eV, and the iterative accuracy convergence value is not less than 1.0 × 10−5 eV/atom for the total force of each atom and less than 0.03 eV/Å for all atomic forces. In addition the high-symmetry k-point path is taken as Γ(0,0,0) → M(0,0.5,0) → K(− 1/3,2/3,0) → Γ(0,0,0) Chen et al, AIP Adv 8:105105, 2018. [ABSTRACT FROM AUTHOR]

Gallium selenide (GaSe) has become increasingly popular in the field of optoelectronics due to its suitable band gap. The layered structure of bulk crystal GaSe makes it easy to create a monolayer of GaSe. However, this also results in an increase in the band gap. In this paper, we used the full-potential periodic density functional theory (DFT) method to examine the electronic structure of both pure and Cu-doped GaSe. We modeled Ga1-xCuxSe with x = 0.02, 0.03, 0.056, and 0.125 with and without Ga vacancy. We compared the structure, electronic properties, and magnetic properties of the pure bulk and monolayer with those of the Cu-doped samples. The density of state graphs clearly demonstrate that Ga-defected and Cu-doped GaSe have p-type characteristics. The presence of a Ga vacancy causes the GaSe monolayer to become half-metallic, which has potential applications in spintronics. When the Cu concentration reaches approximately 3%, there is a 20% reduction in the band gap. Both the Ga vacancy and Cu doping create deep defect levels that lead to carrier recombination. The position of these levels is highly dependent on the concentration of Cu. Increasing the Cu concentration from% 1 to 2.78% results in a decrease in recombination. [ABSTRACT FROM AUTHOR]

The atomic structures, growth patterns, new spintronic, magneto-optic, and electrical properties of 2D armchair nanoribbons of group-IV transition metal nitrides (TiN, ZrN, and HfN) have been investigated. The atomic unit cells of TiN, ZrN, HfN, TiZrN, TiHfN, and ZrHfN have been transformed into the matching armchair nanoribbons. By comparing the proposed nanoribbon to the bulk and monolayer structures of these metal nitrides, the structural stability, density, and projected density of states, band structure, magnetic behavior, and polarization were evaluated. The outcomes demonstrate that, in comparison to the crystalline structure, the suggested systems exhibit ferrimagnetic behavior and a remarkable magnetic moment. Also, a higher magnetic moment of about 24 μB in the supercells of the suggested nanoribbons was discovered due to the increased atom count. The proposed structures demonstrated indirect band gap semiconductor capabilities in the range between 1.66 eV and 2.16 eV which is again an unknown phenomenon in the bulk structure of transition metal nitrides. Owing to these characteristics, the proposed structures can be employed in many optoelectronic applications, such as solar cell devices, LEDs, laser diodes, and optical fibers where the band gap is the key requirement. Apart from this, they can also be useful in coating biomedical implanted chips, transformers, switches, and batteries. Memory storage devices will also benefit from the unique characteristics of the proposed nanoribbon structures. [ABSTRACT FROM AUTHOR]

The electronic, optoelectronic, linear and nonlinear optical (NLO) properties of some corannulenes of formula C5n2H5n (with n = [2,4]), doped with boron–nitride units at the rim position, have been studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. This work aims to substitute B–N units at the rim position in some corannulene structures in order to propose new materials for electronic, optoelectronic and nonlinear optical applications. According to the investigations carried out, the analysis of the cohesive energies of the studied corannulene derivatives indicates that they are energetically stable materials. Based on the |HOMO–LUMO| energy gap values, we find that corannulenes doped with B–N units at the rim position exhibit the same semiconducting nature as the parent structure from which they derive. Moreover, the value of first-order hyperpolarizability (β0) of structures containing B–N isoelectronic units at the rim position in corannulenes is higher than that of the urea molecule considered as a reference molecule commonly used in nonlinear optics (NLO). We hope that the present work will also pave the way for the design of high-performance nonlinear optical materials based on boron–nitride-doped corannulene at the rim position. TD/B3LYP-D3/6–31 + G(d) calculations revealed that among the proposed derivatives, the compounds C35B5N5H15 and C70B5N5H20 exhibit high photo-current response in the visible range. This gives these new materials good performances for optoelectronic applications. Although all the studied properties of the doped structures with B–N units at the rim position are not better than those at the spoke position reported in the literature, these proposed systems have good capabilities to be used as suitable organic semiconductors in the photovoltaic field. [ABSTRACT FROM AUTHOR]

This study investigates the sensing capabilities of (8,0) SWCNTs in detecting formamide (HCONH2), a molecule crucial for the structure of proteins, nucleic acids, and certain anti-cancer drugs. Adsorption of HCONH2 on pristine SWCNT, Al- and N-doped SWCNT, and Al/N co-doped SWCNT was studied using dispersion-corrected density functional theory (DFT-D). Formamide was adsorbed from both oxygen and –NH2 sides, and the structures were fully optimization. The relaxed structures were applied for calculating magnetic and electronic properties like adsorption energies, band structures, and partial density of states. Most negative adsorption energy in doped structures indicates the strongest adsorption of formamide in doped structures than pristine SWCNT. The results also indicates that formamide adsorption does not change the electronic properties of pure SWCNT and N-doped SWCNT. However, it removes the band gaps of Al- and Al/N-doped SWCNT. Therefore, the modified nanotubes convert from semiconductor to metallic character which can be detected using electronic devices. Moreover, formamide adsorption induces some magnetization to Al-doped SWCNT and Al/N co-doped which can be utilized in spin transport devices. These findings suggest that Al/N co-doped and Al-doped SWCNTs are good candidates for detecting HCONH2 molecules. [ABSTRACT FROM AUTHOR]

Adsorption of small Te clusters on tellurene and M o S 2 monolayers have been studied within density functional framework. With adsorption on 2D monolayers, Te clusters show distortion in cluster geometry along with local distortions in the monolayer. Adsorption energy is found to be higher in T e n $ t e l l u r e n e as compared to T e n $ M o S 2 , suggesting that there exists a strong interaction between Te clusters and tellurene substrate. Adsorption of clusters on monolayers results in the modification of the effective band gap of these monolayers. Analysis of the charge density difference profile shows that a certain amount of charge is transferred from the clusters to the substrates. This results in the redistribution of the charge. Our optical calculations for the interband transitions show that Te cluster creates quantum states inside of monolayers, which leads to increasing optical absorption of the system. Additional low-intensity absorption peak, in addition to the main peak, has been noticed in cluster-adsorbed M o S 2 monolayer for E ‖ C. The real part of the dielectric function reveals the existence of plasmon frequencies. We conclude that the cluster adsorption on different monolayers alters the electronic and dielectric properties of monolayers. [ABSTRACT FROM AUTHOR]

Density functional theory calculations have been performed to investigate nH2 (n = 1–4) molecules adsorbed on the pristine and group 8B transition metal (TM = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt) doping on B or N site of boron nitride nanocage (B12N12). The structural stability, adsorption ability, and electronic property of before and after different numbers of H2 molecule adsorption on the pristine and the TM-doped B12N12 nanocages have been investigated. The calculated results point out that all TM atoms display strong binding with B12N12 nanocage in which the Os atom displays the strongest interaction with B12N12. In addition, the pristioptimized geometrical structure of the pristinene B12N12 has a weak interaction with the H2 molecules. For hydrogen molecules adsorbed on TM-doped B12N12 nanocages, the hydrogen molecules can be strongly adsorb on the TM-doped B12N12 with appreciable adsorption energy, in which the OsB11N12 displays the strongest interaction with the hydrogen molecules. Accordingly, the hydrogen adsorption abilities of B12N12 can be significantly improved through TM doping. Electronic properties of the pristine B12N12 are significantly changed after TM-doping, especially the energy gap of the B12N12 is dramatically decreased. Moreover, electronic properties of the TM-doped B12N12 nanocages are noticeably changed after adsorptions compared with the pristine B12N12. Therefore, the TM-doped B12N12 can be used for hydrogen storage and sensing applications of B12N12 nanomaterials. [ABSTRACT FROM AUTHOR]

The vacancy-ordered quadruple perovskite Cs4CdBi2Cl12, as a newly-emerging lead-free perovskite system, has attracted great research interest due to its excellent stability and direct band gap. However, the poor luminescence performance limits its application in light-emitting diodes (LEDs) and other fields. Herein, for the first time, an Ag+ ion doping strategy was proposed to greatly improve the emission performance of Cs4CdBi2Cl12 synthesized by hydrothermal method. Density functional theory calculations combined with experimental results evidence that the weak orange emission from Cs4CdBi2Cl12 is attributed to the phonon scattering and energy level crossing due to the large lattice distortion under excited states. Fortunately, Ag+ ion doping breaks the intrinsic crystal field environment of Cs4CdBi2Cl12, suppresses the crossover between ground and excited states, and reduces the energy loss in the form of nonradiative recombination. At a critical doping amount of 0.8%, the emission intensity of Cs4CdBi2Cl12:Ag+ reaches the maximum, about eight times that of the pristine sample. Moreover, the doped Cs4CdBi2Cl12 still maintains excellent stability against heat, ultraviolet irradiation, and environmental oxygen/moisture. The above advantages make it possible for this material to be used as solid-state phosphors for white LEDs applications, and the Commission International de l'Eclairage color coordinates of (0.31, 0.34) and high color rendering index of 90.6 were achieved. More importantly, the white LED demonstrates remarkable operation stability in air ambient, showing almost no emission decay after a long working time for 48 h. We believe that this study puts forward an effective ion-doping strategy for emission enhancement of vacancy-ordered quadruple perovskite Cs4CdBi2Cl12, highlighting its great potential as efficient emitter compatible for practical applications. [ABSTRACT FROM AUTHOR]

In this computational study, first-principles calculations based on density functional theory are successfully employed to study the linear and nonlinear optical properties of four pyrazole analogues, which are scaffold molecules and influential families of N-heterocycles due to their proven applicability. We calculate and discuss their dipole moment, energy gap, polarizability, and first hyperpolarizability to elucidate the nonlinear optical activity of the four O-acylated pyrazoles in a detailed manner. The theoretical energy gap is estimated at around 2.4 to 2.8 eV. These pyrazoles exhibit efficient hyper-Rayleigh scattering hyperpolarizability, calculated to be 1839.25 and 1834.29 a.u. at the PBE0 and BVP86 functionals, respectively. This investigation shows the potential of these O-acylated pyrazoles as candidates for nonlinear optics applications. [ABSTRACT FROM AUTHOR]

Using ab initio density functional theory with static mean-field correlations, we calculate the Heisenberg and Dzyaloshinskii-Moriya interactions (DMI) for an atomistic spin Hamiltonian for the lacunar spinel, GaV4S8. The parameters describing these interactions are used in atomistic spin dynamics and micromagnetic simulations. The magnetic properties of the lacunar spinel GaV4S8, a material well-known from experiment to host magnetic skyrmions of Néel character, are simulated with these ab initio calculated parameters. The Dzyaloshinskii-Moriya contribution to the micromagnetic energy is a sum of two Lifshitz invariants, supporting the formation of Néel skyrmions and its symmetry agrees with what is usually expected for C3ν-symmetric systems. There are several conclusions one may draw from this work. One concerns the quantum nature of the magnetism, where we show that the precise magnetic state of the V4 cluster is crucial for understanding quantitatively the magnetic phase diagram. In particular, we demonstrate that a distributed-moment state of each V4 cluster explains well a variety of properties of GaV4S8, such as the band gap, observed Curie temperature and especially the stability of Néel skyrmions in the experimentally relevant temperature and magnetic-field range. In addition, we find that electronic correlations change visibly the calculated value of the DMI. [ABSTRACT FROM AUTHOR]

The CsPbBr3 perovskite materials have promising applications in various optoelectronic devices due to their advantages of high luminescence color purity, tunable band gap, and high photoluminescence quantum yield. Herein, the phase stability, electronic structure, and optical properties of CsPbBr3 under rare-earth (RE) doping and hydrostatic pressure have been studied using density functional theory calculations. The relationship between properties of perovskites and different RE doping and pressure was summarized. The band gap of CsPbBr3:RE appeared reduction with the decreasing radius of the doping RE ions, which can guide the adjustment of band gap. The pressure coefficients of undoped CsPbBr3 is − 0.016 eV/GPa, while that of RE-doped CsPbBr3 exhibits an average of − 0.0144 eV/GPa. The combination of RE doping and pressure provides a wider tunable range for band gap. The rare-earth doping and applying pressure are of great significance for the regulating properties of perovskites. Our work provided the opportunities to unveil the underlying mechanism of the doping effect and pressure engineering. [ABSTRACT FROM AUTHOR]

For the last few years technical improvements of compositions and preparation procedures for perovskite-based solar cells have remarkably enhanced their energy conversion efficiency. Crystal and electronic structures together with ion diffusion in partially substituted cubic methylammonium (MA) perovskite based on lead halide MA0.5X0.5PbI3, where X is the cation, are theoretically investigated using density functional theory and molecular dynamics methods. The electronic structure of partially substituted perovskites studied is similar to the MAPbI3 structure, however, the band gap changes compared to their structures. Partial MA substitution distorts the lattice, which prevents MA or X diffusion between A sites in the perovskite crystal. The partial cation substitution affects the electronic structure and distorts the crystal lattice of perovskite, which makes it possible to control the optical properties of the material in different spectral regions and to influence the electronic composition of defects. [ABSTRACT FROM AUTHOR]

Context: The effects of selected substituent groups (-CH3, -Br, -CO2CH3, -COOH, and -NH2) and their relative positions on the electronic and structural properties of mono-substituted naphthalenes were investigated theoretically. In order to elucidate the suitability of the studied substituents in different fields including chemistry, spectroscopy, and materials sciences, accurate DFT calculations were performed at the dispersion-corrected B3LYP level of theory (B3LYP-D3/6–311 + + G(d,p)), and the obtained results were then validated by extensive comparisons with available experimental data. Among the studied substituents, the -NH2 group causes the maximum reduction of the HOMO–LUMO energy gap. This result revealed clearly the suitability of the -NH2 group, compared to other studied substituents, in the chemical synthesis of future organic-semiconductors having small energy gaps. In addition, the level of theory adopted in this study allowed the fine discrimination between the chemical reactivity parameters of the studied congeners, which is very difficult to perform experimentally. On the other hand, the rotational barriers of the studied non-halogen substituent groups were predicted. The greater sensitivity of the rotational barrier heights to the local environments, arising from intra-molecular interactions, was attributed to the -CH3 group. The torsional frequencies, calculated within the harmonic approximation, were also employed to relatively explore the differences between the environments of the same substituent at two different positions. The usefulness of these results can be manifested in the vibrational spectroscopy field, especially, for the IR/ Raman spectral analysis of polycyclic-aromatic congeners. Method: All calculations were conducted within the Density functional theory (DFT) using the so-called dispersion-corrected B3LYP functional (B3LYP-D3) with the carefully selected 6–311 + + G(d,p) basis set. The B3LYP-D3/6–311 + + G(d,p) calculations were performed using the Gaussian 09 program, and the obtained results were visualized by employing the GaussView 6.0.16 program. [ABSTRACT FROM AUTHOR]

Context: A series of five organic dyes (Mi, i = 1–5) of the D-A'-π-A structure were designed based on reference dye (Ref), and the influence of different auxiliary acceptors (A') on their efficiency in dye-sensitized solar cells (DSSC). Methods: Was studied theoretically using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. In this context, the electronic structures, optical properties, and the parameters influencing the power conversion efficiency (PCE), such as light harvesting efficiency (LHE), electron injection driving force (∆Ginject.), and open circuit photo-voltage (VOC), have been evaluated and discussed. The modification of the auxiliary acceptor (A') in the D-A'-π-A structure of the designed organic dyes has the advantage of significantly decreasing the band gap, which leads to the broadening of the absorption band that is red-shifted and improves the photovoltaic characteristics compared to Ref. Theoretical results reveal that M1, and M5 can be used as excellent sensitizer candidates for DSSC applications. [ABSTRACT FROM AUTHOR]

Reducing the thickness of semiconductors to the limit of a few monolayers often leads to emergence of new properties. In this work, the thickness dependence of the band gap of cadmium telluride slabs in both the sphalerite phase and in the inverted phase is studied using the density functional theory method. The sphalerite phase is characterized by Cd–Te–Cd–Te alternating atomic planes, while in the inverted phase the order of planes is Te–Cd–Cd–Te. It is shown that using slabs with a thickness of one to several monolayers variable-gap structures can be fabricated. [ABSTRACT FROM AUTHOR]

Tetragonal graphene nano-capsule (TGC), a novel stable carbon allotrope of sp2 hybridization is designed and doped with phosphorus (P) to study the O3 and SO2 gas sensitivity via density functional theory calculation. Real frequencies verified the natural existence of both TGC and P-doped TGC (PTGC). Both TGC and PTGC suffer structural deformations due to interaction with O3 and SO2 gases. The amount of charge transfer from the adsorbent to the gas molecule is significantly greater for O3 adsorption than SO2 adsorption. The adsorption energies for TGC + O3 and PTGC + O3 complexes are − 3.46 and − 4.34 eV respectively, whereas for TGC + SO2 and PTGC + SO2 complexes the value decreased to − 0.29 and − 0.30 eV respectively. The dissociation of O3 is observed via interaction with PTGC. A significant variation in electronic energy gap and conductivity results from gas adsorption which can provide efficient electrical responses via gas adsorption. The blue/red shift in the optical response proved to be a way of detecting the types of adsorbed gases. The adsorption of O3 is exothermic and spontaneous whereas the adsorption of SO2 is endothermic and non-spontaneous. The negative change in entropy verifies the thermodynamic stability of all the complexes. QTAIM analysis reveals strong covalent or partial covalent interactions between absorbent and adsorbate. The significant variation in electrical and optical response with optimal adsorbent-gas interaction strength makes both TGC and PTGC promising candidates for O3 and SO2 sensing. [ABSTRACT FROM AUTHOR]